I added tags to this post to increase visibility.
To look into possible causes of this error message we will need a copy of your method and a data file collected with this method.
I just had a similar (same?) issue on a 7890B-5977B system which seems to be fixed. We save the method with data file and looking at that method (in the data folder) I noticed that there is an "endless loop" of nested *.M and *.D folders within the data folder. I then looked at the parent method (I'll call it method.M) and there were multiple nested method.M and data.D folders. I removed the interior nested method.M folder from the parent method.M and everything seems to be working. As to why the nested *.M and *.D folders came to be in the parent method folder I don't have a clue.