The only time I have seen this symptom, and it happens in Windows on a true Windows computer too, is when the "Send Header With Each Job" option is unchecked.
Changing PostScript Header
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1) Open the Printers control Panel
2) Click on Setup
3) Click on Options
4) click on the box that reads "Send Header With Each Job". When an 'X' appears in the box, it sends the header with each job.
Make sure the box is checked and try printing again.
I have tested SoftWindows with system software 7.5, and it prints fine from Windows. In addition, I unchecked the "Send Header With Each Job" box and tried to print. I did not get the error message that you did on the screen, instead the error message was printed and I received a general "PostScript Error" from PrintMonitor. So, checking the box should correct the problem.