A CAD block download stuck or keeps failing: a checklist

Confirm it's actually stuck, not just slow

Before troubleshooting anything, check whether the download is genuinely stalled or just moving slower than you're used to. A block zip is typically small, well under a few megabytes, so on any reasonable connection it should complete in a second or two, but if your browser's download manager shows a progress bar frozen at the same percentage for more than about ten or fifteen seconds with no movement at all, that's a real stall rather than normal slowness, and it's worth working through the checklist below rather than waiting it out.

Rule out your network connection first

This sounds obvious but it's the single most common cause and the easiest to check, open a completely unrelated site or run a quick speed test to confirm your connection is actually up and responsive right now, not just showing a wifi icon that looks connected while actually being flaky. Public wifi in cafes, hotels, and co-working spaces is particularly prone to this, where you appear connected but the actual throughput is inconsistent or a captive portal is silently blocking file downloads specifically while normal browsing still works.

If you're on a VPN, especially a corporate one, try disconnecting it temporarily and retrying the download. Some VPN configurations proxy and filter file downloads more aggressively than regular web traffic, and a stall or failure that only happens with the VPN on but not off points squarely at the VPN's filtering rather than anything on the source site's end.

Check for an ad blocker or privacy extension interfering

Ad blockers, script blockers, and privacy extensions occasionally interfere with the download trigger itself, particularly ones set to an aggressive blocking level that strips scripts a site needs to initiate the file transfer cleanly. If a download button does nothing when clicked, or starts and immediately fails, try temporarily disabling your ad blocker for that site specifically, or open the page in a private or incognito window where extensions are typically disabled by default, and see if the download completes normally. If it does, you've isolated the cause to that extension, and you can whitelist the site rather than disabling the extension entirely going forward.

Try a different browser to isolate the problem

If disabling extensions doesn't help, the next fastest isolation test is simply trying a completely different browser, Chrome to Firefox, or Safari to Edge, whatever you have installed. Browser-specific download manager bugs do happen, particularly after an update introduces a regression, and if the same download completes cleanly in a second browser but consistently stalls in your usual one, that tells you the fix is on the browser side, clearing that browser's cache and download history, or in stubborn cases reinstalling it, rather than anything about the file or the source.

Check your available disk space

It sounds almost too simple to mention, but a downloads folder or a hard drive that's essentially full will cause downloads to fail partway through with an error that doesn't always clearly say "disk full," sometimes it just reports a generic write failure or silently stalls instead. Check you have a reasonable amount of free space, and if your Downloads folder has years of accumulated clutter, clearing some of it out is worth doing anyway and occasionally resolves stalls that had nothing obviously to do with space at first glance.

If everything else checks out

If you've confirmed your connection is solid, tried a different browser, ruled out extensions, and disk space isn't the issue, and the download still consistently fails at the same point, that's the point where it's worth trying again after a short wait, since transient server-side hiccups do happen briefly during traffic spikes and usually resolve within a few minutes on their own. Working through the checklist in this order, network, extensions, browser, disk space, before assuming anything is wrong with the file itself, resolves the overwhelming majority of stuck or repeatedly failing downloads without needing to guess.

Mobile devices and antivirus scanning can both interfere too

If you're trying to download a block on a phone or tablet rather than a desktop, downloads fail there for a slightly different set of reasons worth knowing about, mobile browsers often handle zip files differently, sometimes routing the download through a separate downloads app entirely rather than saving directly, and background app restrictions on both iOS and Android can interrupt a download if you switch apps mid-transfer. If you're consistently hitting failures on mobile specifically but not on desktop, that's a strong signal the issue is mobile-specific handling rather than anything about the file or connection, and downloading on a desktop or laptop first, then transferring the file across if you need it on the tablet, sidesteps the whole problem entirely.

On desktop, real-time antivirus scanning is worth checking too, it occasionally intercepts a download mid-transfer for inspection and, on a slower machine or with a large scan queue backed up, that interception can look identical to a stalled download even though nothing is actually broken, it's just queued behind a scan waiting its turn. Temporarily pausing real-time protection for the duration of one download, then turning it straight back on, is a reasonable way to test this if nothing else on the checklist has explained the stall, and it's a more common cause on older or lower-spec work laptops than on a fast modern machine.

A DNS resolution problem is worth adding to the checklist too, even when general browsing feels fine, since some sites resolve through a content delivery network that occasionally has connectivity hiccups isolated to specific DNS providers while the rest of the internet is working normally for you. If a download consistently fails specifically on one site while everything else browses fine, and you're comfortable making the change, switching your DNS to a public resolver like 1.1.1.1 or 8.8.8.8 in your network settings, then retrying, rules this out in under a minute and occasionally resolves stalls that looked for all the world like a problem with the file itself.

On a corporate network specifically, firewall rules sometimes throttle or block traffic to specific file types or domains without any user-facing message at all, the connection just quietly times out rather than failing with a clear error. If downloads consistently stall only on the office network and work immediately from home or on mobile data, that's a strong signal worth raising with IT directly rather than continuing to troubleshoot on your own end, since it's a network policy decision rather than anything fixable from your browser settings.