This is due to a corrupt log file at the file path destination \\SERVER\prodisk\proclaim\_docs\NewScreenContents.txt.
Navigate your _docs folder on your server. This is often located in \\SERVER\prodisk\proclaim\_docs.
Locate the NewScreenContents.txt file.
Rename the file to NewScreenContentsCorrupt.txt.
Log out of Proclaim.
Log back in to Proclaim.
Test by opening Screen Designer.
The issue should no longer be present.
If this does not work, please ask a question in the MyAccess Portal Digital Assistant and ask to "Speak to a human" to be put through directly to our support team.