>>>Did you test your PDF2PS function standalone?
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>>Yes, If I am not using Parallel Fox the same is running Fine. It seems to me that when there is One CPU involved, the DLL is not shared and may be when there are more than One CPU there may be Sharing Problem of DLL , so error might be generated. Is it so ?

If you're sure that this code works fine if not running parallel, one of the possibilities is to wrap the code to call this function in try/catch block and retry in case of the failure the second time.