This happened when I synced from my laptop after adding one item with attached PDF and then synced to a desktop PC at work. The error came on the desktop PC.

I can't see anything wrong with the database, though, at least not yet.

============
Error log:

[unrelated errors removed — D.S.]

[JavaScript Error: "Win error 2 during operation open on file C:\Users\[…]\Zotero\storage\TEPW2E75\.zotero-ft-unprocessed (The system cannot find the file specified.
)" {file: "chrome://zotero/content/xpcom/fulltext.js" line: 976}]
Zotero.FullText resource://zotero/bluebird/util.js:16:16
module.exports/PromiseSpawn.prototype._promiseRejected@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/generators.js:106:18
module.exports/Promise.prototype._settlePromise@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:576:17
module.exports/Promise.prototype._settlePromise0@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:614:5
module.exports/Promise.prototype._settlePromises@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:689:13
Async.prototype._drainQueue@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:133:13
Async.prototype._drainQueues@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:143:5
Async/this.drainQueues@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:17:9


[JavaScript Error: "Win error 2 during operation open on file C:\Users\[…]\Zotero\storage\4YWYGWFV\.zotero-ft-unprocessed (The system cannot find the file specified.
)" {file: "chrome://zotero/content/xpcom/fulltext.js" line: 976}]
Zotero.FullText resource://zotero/bluebird/util.js:16:16
module.exports/PromiseSpawn.prototype._promiseRejected@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/generators.js:106:18
module.exports/Promise.prototype._settlePromise@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:576:17
module.exports/Promise.prototype._settlePromise0@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:614:5
module.exports/Promise.prototype._settlePromises@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/promise.js:689:13
Async.prototype._drainQueue@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:133:13
Async.prototype._drainQueues@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:143:5
Async/this.drainQueues@resource://gre/modules/commonjs/toolkit/loader.js -> resource://zotero/bluebird/async.js:17:9

[JavaScript Error: "Download request 1/ESSCAREE failed"]

[JavaScript Error: "Win error 5 during operation remove on file C:\Users\[…]\Zotero\storage\ESSCAREE\Mainhard et al_2009_A model for the supervisor–doctoral student relationship.pdf (Access is denied.
)" {file: "(unknown module)" line: 0}]

version => 5.0.60, platform => Win32, oscpu => Windows NT 10.0; WOW64, locale => en-US, appName => Zotero, appVersion => 5.0.60, extensions => Zotero LibreOffice Integration (5.0.14.SA.5.0.60, extension), Zotero Word for Windows Integration (5.0.11.SA.5.0.60, extension), ZotFile (5.0.9, extension), Zotero DOI Manager (1.3.7, extension), Shockwave Flash (20.0.0.306, plugin)