Missing 'valid to' date in timestamp conversion.

What causes this issue?

The partner role assignment validity end date is missing.

System Response

System cannot proceed as internal timestamp cannot be generated.

How to fix this error?

If the validity end date has not been entered, please enter this
before proceeding. If this has been entered, an internal error has
occurred - please notify your system administrator.

Error message extract from SAP system. Copyright SAP SE.