Can you indicate which OPM version? If it is not 10.4.4, then I can offer suggestions as to the cause based on what fixes have occurred.
I suspect reinstalling isn't going to solve this problem as it is most likely a project-specific issue - especially if reverting changes will resolve it. There is no logging in OPM.
I know I am replying late, but: It turns out that two of us were using different versions. He was using a later version than me. I guess he used a function that was not available in my version.
One issue that is really bugging me about OPM is that it will tell me that there is an error, but it gives no indication what rule file is causing the problem. There was some other issue recently in which OPM blew up and I had to spend a lot of time figuring out what the problem is.
This particular exception is not being reported by OPM - it is being reported by the underlying .NET framework, so OPM does not know which rule file is causing the problem. In order for us to improve the OPM errors, it would be useful to know which "different versions" were being used, and if indeed you did figure out the cause of the problem. If you are able to provide any further details, then they would also be appreciated.