Protege hanging when saving ontologies

[AlasdairGray]

My students are using Protégé 5.5 and are experiencing it hanging when they try to save their ontology. This is happening on both Windows and Mac machines. The students have now reverted to Protégé 5.2 and this has resolved the problem. The challenge is that this is only happening for some students, but the ontology that they try to save does not seem to be the issue.

[jessi678]

Here is a log file for the issue on a Windows machine.
protege.log

Below is the last log after Protege 5.5 crashes from saving an ontology (from Show Log and can be seen in log file:
Cannot generate ontology catalog for ontology at http://www.semanticweb.org/jessi/ontologies/2021/0/untitled-ontology-2. URI scheme is not "file"