This error is related to the revert functionality. You can probably click OK and ignore it and wouldn't have problems unless you tried to revert later.
We will have to investigate this more to see the root cause. What operating system and DW version are you using? We'll try to reproduce the problem and fix it sometime early next week. It appears to be a bug, but we did lots of testing with powerstore 3, so we may need more information or to create a support incident to help us diagnose the cause until we can reproduce it.