Invalid Parent Theme

[fwp]

I would like to experiment with different themese, but when I select most of them I get the error message: "The theme "<theme-name> has an invalid parent theme specified in the configuration file themes.ini. It cannot be selected". Is there a way I can solve this problem?

[pinbrook]

Possibly reinstall the software

[fwp]

That seems to have worked (I tried "repairing" it first, but that had no effect).

Many thanks

Francis