Unable to Sharpen any photograph

[Rascal]

I seem to have a problem with Corel PSP, version 14.1.0.5, when I attempt to sharpen a .jpg image. I open the file, select Adjust/Sharpeness/Unsharpen Mask.
I have Preview on Image ticked. The photo sharpens for a few seconds then reverts back to the original sharpness. This applies to all my photographs,I cannot save the sharpened image. I have tried a re-install, it made no difference. Any help appreciated.