Class type & : class & locked by user &

What causes this issue?

You want to edit the allocation to a class. This requires that the
class is not changed in the meantime. However, another user is already
processing the class or its allocation.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Try again later.

Error message extract from SAP system. Copyright SAP SE.