The client has several api groups where they are unable to remove api's from the api group. They will disable the API, then go into the API Group and click the 'Remove' button. They will then hit the 'Save' button and the following error will be generated:
The request could not be completed due to processing errors.500
This situation was only seen when the api group was associated with a large number of applications. In this particular use case the api groups that experienced the problem were tied to 500+ applications.
Our development team has created a fix for this situation which will be included in the Portal 5.1 version. If you are experiencing this problem please look to upgrade to Portal 5.1 or later.