Theme replacement gone wrong, Grid Type error

I tried replacing the theme for a phone app with a theme from a seperate module.

I put in the new theme, but once i deleted I got hundreds of errors of the following type:

Invalid Use Of Grid Units
'Margin Top' must be set in px, pt, or %. To use grid units you must set the theme's 'Grid Type' property to 'Fluid' or 'Fixed'.

The strange thing is that the new theme already had grid type Fluid (inherited from "PhoneTheme", but same problem if it is set manually).The same goes for "BaseTheme" and "PhoneTheme".

Any idea what could be the problem here?


I already managed to figure it out.

I had yet to fill in the Default Theme for my module.

Doing that solved my errors.