This was a bug in the Citavi importer that resulted in some bad data ending up in the page number field. We've fixed this in the importer in the Zotero beta, and the fix will be included in Zotero 6.0.5. The error message from the server tells you the relevant attachment item key, so unless many items of yours were affected, rather than reimporting (which would create duplicates) you can go to the library root, paste the 8-character key from the error message into the search bar in All Field & Tags mode to find the attachment in question, find the annotation with the invalid page number in the annotations sidebar, and double-click on the page number to edit it.

thanks, but now the error report ID is 508104202