Hi,
I have encountered the same issue.
Apparently while we put an illegal value in customizing causing this error to happen.
we did the following:
1. go to spro > sap solution manager > capabilities (optional) > change request management > cha nge request management framework > make settings for change transaction types
2. choose transcation type from list and go to "assign actions" on the left.
3. all actions that are in this list are supposed to come from the search help by pressing F4 and not by pasting. the search help protects you from putting illeagle values.
Hope This helps.
Amir.