That must be a Bug in XMM that die Value of the Variable is not reset for every Movie the Script is used. It can't be a script problem. So Ale has to fix that bug.
You can add a Option in how many Actors are imported your self simply edit the line 51 of the IMDB.COM(Complete) Script from:
#SETOPTION#=#92#999[Number of Actors to import]4=Actors|8=Actors|12=Actors|99=Actors|999=Actors
to for example:
#SETOPTION#=#92#999[Number of Actors to import]4=Actors|8=Actors|12=Actors|30=Actors|99=Actors|999=Actors
Now you can choose the 30 as a new number in the Advanced Options.