Paradox 10: Can't (re) size window

[kostenzer]

I made something in paradox 10, years ago.
Now changes are needed.
This went well, BUT the form windows have to be resized, they must be made bigger.
I can't manage this nor bigger, nor smaller.

I tried:
- opening form
- design form
- changing size by mouse

In the object explorer FullSize and Size change while changing size by mouse.
In front of FullSize is a locked symbol. Manual change that size is not possible.

Does somebody know a/the solution?

Thanks

Rob