Problem when changing from plainfile store to rcs

I have a Foswiki instance and at first the store option used teh Plainfile. I then change the store system to use rcs.

Following this I am able to create new topics and save them with the rcs versioning.

However with the topics that were editing dutin the Plainfile store I am unable to save any changes to rcs.

Error saving topic
During save of Sandbox.TestRcs an error was found by the version control system. Please notify your Foswiki administrator.
Operation save failed with an internal error
Go back in your browser and save your changes locally.

I have tried to remove the Plainfile pfv directory of the file but this does not help. I have also cleared the cache. What else can I do to allow the save under rcs?

-- LlewelynJones - 17 Jun 2021