Hello, i noticed that my PNG's from a dopus JPEG->PNG conversion cannot be opened in PaintShopPro 7 but in HyperSnap 6. After editing the PNG in HyperSnap and saving the edited image again to PNG format, this newly created PNG can be opened in PaintShopPro 7 without problems.
From this observation i conclude that PSP7 is pickier with what it considers "a valid PNG". I don't know about higher versions of PSP, probably the company (Jasc) doesn't exist anymore.
Well. Just wanted to share this. Maybe someone else had observed something similar with his/her image editing software.