You are probably using an newer version of Assura than your
parasitic models are create with.

You have to run 'capgen', this is the tool to create parasitic models,
to re-generate them.

Have a look at the files 'RCXspiceINIT' or 'RCXdspfINIT', of your
Assura technology directory, in the last lines of these files the
capgen options of the capgen last run are indicated.

I also strongly recommend to read the chapter
'Assura RCX and Capgen Setup' from the
'Assura Physical Verification Developer Guide'
for better understanding.

Bernd