(1) Does C:\Users\David\Desktop\Work\Zotero Data\storage\4FSWT8F5\6.css already exist? Can you delete it? If it doesn't exist, is that directory writable (e.g. can you create an new text file there)? Do you have any security software running? Try disabling it.

(2) I'm confused why you're using both manual library transfers _and_ syncing. If you're doing this to avoid syncing files, then you should disable file syncing. Otherwise, I'm not sure what you're trying to accomplish.

But presumably that's what's creating this problem?

Yes, that would do it.

I wanted to have an additional backup that I could access remotely online

That's reasonable, though note that zotero.org is not a great backup solution. If you make some undesired changes and sync to zotero.org, there's no way to recover an earlier version of your library from zotero.org. You're better off setting up some third-party service to back up your Zotero data directory.

Is there a reason why you don't want to use sync between your two computers? Do you have a particularly large PDF library and you want to avoid paying for online storage? Considering that you're syncing your library anyway...

I am using the zotero Firefox add-in from different pcs, a Win 7-Pro x64 desktop at home and a Win 7 Home Premium x64 laptop on the road. Firefox is installed (not a portable/usb version) in both cases. The add-in shows its version # to be 4.0.23.1 for both. The same AV software (WebRoot) runs on both. (No, it will Not be disabled. That's silly.) On both machines the zotero storage is with the %AppData%\Mozilla\Firefox\Profiles directory. In both cases I am an administrator. In both cases I have full read/write permissions on the entire %AppData%\Mozilla directory and, in fact, am the owner of that directory in each case as well. So, there are no issues on either box with permissions for the zotero storage, nor are any folders for that storage "custom" in any meaningful sense. Yet, when syncing, the desktop version behaves as expected but the laptop version gives the error "the file .... cannot be created". The laptop has been rebooted several times with the same result. FYI, sync'ing used to work fine on the laptop. I have checked the registry on the laptop for 'zotero' entries; there was one fossil for Windows Explorer file extensions (an HKCR/zotero EditFlags value)left over from an older Zotero Standalone installation that had been uninstalled (via Control Panel). That entry was deleted and the laptop was rebooted; same errors on sync'ing result. Also, a Reset of zotero storage from the server on the laptop has been performed. Initially, it reports that the sync'ing is done, but the little green, circular arrow for the Sync keeps whirling after said report until, very shortly, the same sync error appears. I am at wits end.

no one runs Windows without AV (Linux is another matter); in any case, please note from the post that the very same AV software (same vendor, same vendor's version) is running on both the laptop and the desktop; one has sync'ing issues (the laptop), one does not; so it is most unlikely that disabling the AV is a promising testing scenario;

zotero's problematic sync'ing behavior and its error reporting looks like zotero is interpreting a "read only" Windows folder property (as one would see it in the property sheet in Windows Explorer with a filled, but **unchecked** box, e.g.) as though it were a Read Only permission issue. The folder "read only" property--which almost every folder on the system has (e.g., %Temp%)--is set by the OS and is quite unrelated to permissions per se. Any file in the folder, like a sync'd 'png' or 'gif', with an archival property set will trigger the setting of this "read only" property for the entire containing folder, while having absolutely no effect on true permissions. Any way, that's the behavior as I have seen it.

Re: read only, if the problem were as you described, basically every person using Zotero on Windows would have issues. They don't. It's generally limited to people with seemingly overzealous security software.

(You may be right that XULRunner — the Mozilla platform Zotero is based on that actually performs the file operations — misinterprets the read-only flag, or doesn't take steps to override it the way some other software does. We can look into that and possibly report a bug upstream. But generally, every time we see this it's due to either security software, using Zotero on a network share, or genuine permissions problems.)

Hello,

Same problem here

"The file 'C:\Users\##my username##\AppData\Roaming\Mozilla\Firefox\Profiles\rkqlqu9p.default-1414840171976\zotero\storage\78NGIA2W\Is the haematopoietic effect of testosterone mediated by erythropoietin The results of a clinical trial in older men - Maggio et al. - 2013 - .pdf' cannot be created."

I had the same error for another entry, which I then deleted from the library on the server before syncing again, but it did not help, it hooked at this one the next time. I also tried to shorten the filename (which was created in Zotero). All entries worked fine on my previous Zotero installation (also plugin on Firefox, same system + version).

I never had problems with syncing ever (long time user), just after I reinstalled Firefox and Zotero on my system today, this appeared.

Win 7 pro x64, Zotero V 4.0.23.1. Tried disabling security software (Mc Afee) as recommended above etc., no success.

Any idea what could help?

Thanks!

Yeah, and if you're still having trouble with the beta or 4.0.24, start a new thread, since your issue is different from the one above. But assuming your username is eight characters long, the beta or 4.0.24 should fix this.