When rebuilding the link database or rendering an item with a "general link" field, the following error can occur:
System.FormatException: Unrecognized Guid format. Actual value: ---> System.FormatException: Unrecognized Guid format. at System.Guid.GuidResult.SetFailure(ParseFailureKind failure, String failureMessageID, Object failureMessageFormatArgument, String failureArgumentName, Exception innerException) at System.Guid.TryParseGuid(String g, GuidStyles flags, GuidResult& result) at System.Guid..ctor(String g) at Sitecore.Data.ID..ctor(String id)
The error appears if some "general link" field (or deprecated "link" field) contains an empty "ID" attribute in its raw value, or doesn't contain it at all.
Download and install the corresponding fix depending on your Sitecore Experience Platform (XP) version:
See the readme.txt file inside the archive for installation instructions.
After applying the fix, you must not install any Sitecore XP updates until Sitecore includes the changes associated with the hotfix in a public update.
You can find more details about hotfixes here: KB0077333
In case the fix cannot be installed for some reason, you can use another solution:
Unlike the hotfixes mentioned above, FixLinks.aspx from Sitecore.Support.203014.zip fixes the existing corrupted links in the master database.
In order to fix the issue for the web database, republish the site after FixLinks.aspx finishes its work.
If new problematic links appear, the page should be launched again.