Did you request it to be read-only? That protects it from being changed. You have to remove that protection to change it and then re-apply afterward.
Also, you cannot export patterns to PCStitch 7 format if you use any stitched fonts or library motifs unless the font and/or library was entirely of your creation in the first place.
The way PCStitch 10 protected copyright protected patterns is to make them read only. That locks them from being changed. It is not the normal Windows "Read-Only" attribute but in the file itself.
If this is not what is happening, then contact Mark on the issue.