Morover, it seems that the decision whether to proceed or rollback needs 
to be done per attribute. It seems to me that validation messages 
(warning and/or error) directly in the "Add MBean Attributes" 
incorporating the analysis of the implementation class would be the best 
solution. It would be less intrusive, more clear (no need to read the 
mesage of dialog, the feedback could be provided directly in the table 
with colors and/or badging), actions can be done directly in that mode, ...

A pop up is fairly acceptable now; What I suggest here, would be 
probably percieved as an optimal state for the NB integration.