rolling back a transaction

When I try to roll back a transaction after some print actions I get the below error message (see attachment)…

What can be wrong here?

hmm, to fix this i really need a solution that demonstrates this
(very hard to get it repeated)

I don’t know what it was. But I rewrote the method and the message has gone (with the wind). Tested it about 20, 30 times and I didn’t see the message anymore…