[I know I don't have any tags longer than 25 characters, though.]

Mark and Jon: This is likely just due to server load from people with large databases doing initial syncs, causing other connections to time out (hence the "internal server error" part). We'll be making some changes in the next few days to keep the heavier processing from disrupting normal syncing. I'd be surprised if you weren't able to get a sync through at all, however, unless your copies of Zotero are also trying to upload lots of new data (which they shouldn't be if you've been syncing regularly). You can check debug output (or just check for upload traffic in a network monitor) to see.

Having the same problem after resetting my data and trying to replace server data with my client data (was moving Webdav servers do opted to do everything clean).

Hope that the problem gets resolved soon,

Jim

I reset server data, so my copy of Zotero is trying to upload lots of new data.

Ah, right—missed that.

It would be off-putting to new users with hefty libraries to find that they can't sync after all. It might help to be able to sync in chunks (as with storage sync).

That's a possibility we've considered and are still considering, but it would complicate the sync logic. In the immediate future, we'll be switching to doing syncs over a certain size asynchronously, storing the uploaded XML on the servers and processing it as resources allow, which should be within a few minutes. The client will get an immediate response after the upload and then check in periodically until it receives the results of the sync, which it will then display as usual.

I think it would be good to put a warning somewhere that it no longer is a piece of cake to reset server data and start afresh. I'm still getting the error. Can you recommend a time of day when the server isn't overloaded? I'm in another timezone (Amsterdam) so that should work, shouldn't it?

I think it would be good to put a warning somewhere that it no longer is a piece of cake to reset server data and start afresh

I'm not sure what you mean by this. You can now restore from either direction automatically in the preferences. (If you really want the menu options back, you can create a boolean extensions.zotero.sync.debugMenu pref in about:config and set it to true.)

Can you recommend a time of day when the server isn't overloaded?

For the most part the servers aren't really overloaded at all (I suggested that as a possibility because I thought you were doing an incremental sync), but there's a timeout of a few minutes on sync attempts that you might be hitting. Has the size of your library increased markedly since when you first synced to the server in the Sync Preview? How many items do you have?

Dan, what I mean is that since I upgraded to 1.5b and did a 'reset server data' from my clients, I cannot sync anymore. It just stops after some time with 'Invalid response from server'. Most recent try: 1974408103.

From your first reply I gathered that it probably wasn't due to a problem on my side (tags or something). That wouldn't make sense anyway since nothing much has changed since the last time I synced successfully (again, except for the server data reset).

So I'm just looking for the reason I still can't sync — if it's not server overload either, what could it be? And are users that are new to syncing with libraries of the same size (mine is only 1722 items) running into the same problem?

Mark, same problem here. I do have 12,000+ entries though. Firefox freezes for 15-20 minutes every time it tries to perform the first sync to the server. It's been trying dozens of times over the last couple of days, but fails every time.

jlanders, I, similarly, have been waiting to promote Zotero with a blog post, but want it to be working well for me first. :)

I've been also getting the 'invalid response from server error'. I don't know if this was purely accidental, but once I cleared Firefox's error log everything seems to be working fine.

I made some optimizations overnight that should allow some larger syncs in both directions to complete (though probably not yet for 12,000+ items, philgons). Many more to come.

Works like a charm! Thanks.

Er, I think i was able to sync successfully once after the upgrade, rather.