To sumarize, you have been able to decimate without any troubles your Tools in ZBrush 3.5 R3, you switch to ZBrush 4, installed Decimation Master for ZBrush 4 and each time you preprocess, you have this error, right?
Then, some questions
- Does it happen just after clicking on the preprocess button or at a specific stage of the processing?
- Are you running a 64 bits OS?
- if yes, how much Gb of RAM do you have?
- if no, same questions
- How many polygons have your model to preprocess?