I have Analogic cPCI-14-2 DAQ cards in the PXI box. Their driver is a dll for which I wrote LabView interface using LV5.01 . Everything was nice until I switched to 5.1, now it is impossible to run the program for more than 5min without a memory access violation error and subsequent LV crash. I compiled executable from the DAQ module under 5.01 and 5.1. Executable made under 5.1 would not even execute once, resulting in the crash. Then I saved VI's using save as LV5.0 option, compiled executable under LV5.01 and that runs without problems. I ended up using ActiveX server capabilities of the executable by calling it from my main program written using LV5.1 because I needed to call Matlab. ActiveX server is actu ally nice because of DCOM in NT boxes, I can now run everything from my office super-duper machine instead of using a PXI box's Pentium233. Question is, has anyone else had problems with dll calls and how were they solved ? I will appreciate your suggestions.