You cannot reverse this transaction ...

What causes this issue?

The asset line items belonging to this transaction were already
reversed or are themselves reversal postings. In either case, the
system does not allow another reversal. Reversed documents and the
reversal documents for them are automatically marked as such, and
you cannot process them further.

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?

Check your choice of document. If you really need to reverse this
document, then you have to manually post a document with reversed
positive/negative signs from the original posting (back out the
posting) rather than posting a reversal.

Error message extract from SAP system. Copyright SAP SE.