when exactly are you getting that message?
The reason you're getting it is almost certainly because the filename with path is too long for Windows. Zotero should be handling this more elegantly, not sure why it doesn't in this case.
You could try to see what is in that folder -- C:\Users\martheia\AppData\Roaming\Zotero\Zotero\Profiles\rbs1vpcc.default\zotero\storage\EG8VRGMG -- and consider just deleting it <i>from within Zotero</i>, i.e. not in your files system/Windows Explorer.

An alternative would be to move your Zotero data folder to a location with a shorter filepath (that's a setting under advanced in the Zotero preferences and you'd also have to move the files in the data folder after changing that setting, so it may be a little more involved than you'd want it to be).

for some reason two debug windows appeared, posting them both here:

D824967465.

D974155464.

Ok, two immediate challenges on my behalf:
I have looked in my zotero and cannot find the attachement there - or else I would be happy to delete it. I cannot make sense of that path, so I have no clue where to delete.

I am trying to sync with firefox (its crash after an update was what prompted this whole new sync), but I keep getting the same response there - but with a different path name:
message when trying to sync with firefox
The file 'C:\Users\martheia\AppData\Roaming\Mozilla\Firefox\Profiles\37v44h1t.default\zotero\storage\CTU2GKM7\site=hdc+affiliate=ahdcmain+safhdc=sahdcmnnws+ch=national+pg=article+artid=1.314644+adsize=300x250+adpos=01+dcdivname=dclk_objects_06+tile=2059766589+usertype=1' cannot be created.

debug ID for that failed operation is:
D1988461014.

Hi, working to sync via firefox har caused the same kinds of problems today.
Working in 4.0.23.1.

Debug ID
D610027204.

I know that you want me to delete the file from within zotero, but the path it lists is not familiar at all. And when I follow the parent directory that zotero shows me, this seems like a really weir folder - pictures and stuff that I have never added to my zotero library. Again, I know you want me to delete from within zotero - but since I can't figure out what folder it is referrjing to when it claims a file cannot be created I thought I see in the windows directory if there was any hint there as to where in my library the problem file was. I don't know if this makes it any easier for you to speculate what might cause the problem, but the file name suggest to me that something has been corrupted somewhere along the way. But I have no clue as to what to do to remove it, then. Suggestions?

omg! I love you! It seems to work! thank you!

I' having what seems to be the same problem

When trying to sync a fresh zotero install I repeatedly get errors, like:

The file 'C:\Users\Thomas\AppData\Roaming\Mozilla\Firefox\Profiles\3gg7yfz2.default\zotero\storage\2H572UTX\diggthis.js' cannot be created.

Check that the file ...

The file 'C:\Users\Thomas\AppData\Roaming\Mozilla\Firefox\Profiles\3gg7yfz2.default\zotero\storage\2H572UTX\mbox.js' cannot be created.

Check that the file ...

I had the error in the the most recent stand alone release of Zotero. Now i'm on the most recent beta (4.0.25-beta.r7+496d4c5) in firefox, as this was a suggested fix in another thread, and I'm still getting the errors. I choose not to reuse the standalone dir's when installing firefox beta version.

Also tried disabling security software, running as administrator, etc. with no luck.

When I open the parent dir of the culpritt file it apears that some files have been downloaded into the dir so it seems to be an issue with only some of the files.

I'm on windows 7.

Anyone?

Ok - I just disabled my firewall - I'll dig in and see if I can find some other some other blocking security process that I can disable.

obviously you don't want to permanently disable your security software, though, so ideally you'd just find a way to whitelist Zotero.

I've experienced the same issue. None of the solutions suggested have worked to date:

I've disabled the antivirus software (Avast) and the firewall (Comodo); I deleted the directory and re-started the sync but it comes back with the same message after copying one or two files to the directory.

Error Report ID: 2101555784

Thanks, Adam:
I tried again, this time re-booting and removing Avast from the startup menu and then exiting Comodo. The sync worked! I had previously killed both processes (generating the usual Windows warnings about lack of protection) but it must have still left something running that prevented Zotero writing to the directory. Given that these are commonly used security programs, I wonder if anyone has a suggestion on tweaking them to prevent them from blocking Zotero?

(Comodo was also involved in the recent Superfish uproar: http://arstechnica.com/security/2015/02/security-software-found-using-superfish-style-code-as-attacks-get-simpler/ )