Hi all. Just trying to sync my Zotero library, as I have done many times in the past, however now it throws an error when trying to sync. The contents of the error are:

[JavaScript Error: "reader is undefined" {file: "chrome://zotero-night/content/zotero-night.js" line: 919}]

[JavaScript Error: "reader is undefined" {file: "chrome://zotero-night/content/zotero-night.js" line: 919}]

[JavaScript Error: "Error 500 for item GU63FTRL in My Library:

ZoteroObjectUploadError: An error occurred"]

[JavaScript Error: "An error occurred" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 1357}]

[JavaScript Error: "Error 500 for item 68TRMDNZ in My Library:

ZoteroObjectUploadError: An error occurred"]

[JavaScript Error: "An error occurred" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 1357}]

[JavaScript Error: "Made no progress during upload -- stopping" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 1416}]

[JavaScript Error: "Made no progress during upload -- stopping" {file: "chrome://zotero/content/xpcom/sync/syncEngine.js" line: 1416}]

version => 6.0.15, platform => MacIntel, oscpu => Intel Mac OS X 10.16, locale => en-GB, appName => Zotero, appVersion => 6.0.15, extensions => Night for Zotero (0.4.16, extension), Zotero LibreOffice Integration (6.0.2.SA.6.0.15, extension), Zotero Word for Mac Integration (6.0.3.SA.6.0.15, extension), Better BibTex for Zotero (6.7.29, extension, disabled)

Can anyone shed any light on this? Things have been fine until today - I cannot find what has changed.