Pro pack doesn't use bum's. It uses the jpg files. If you have any MAT's that call for a non-existing bum, try running Correct Reference and the problem will be fixed. But be aware that Correct Reference most likely will tak a LOT of time the first time you use it. You can get it in Free Stuff I think.

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.