Can you give any pointer as to how you can replicate such an error ?
I have 7.10 ( build 12325 ) and that only offers UDN2981A and UDN2981A but both seem to work it as would be expected. Those seem to be part of the Proteus provided ANALOG.LIB library and there's no UDN*.MDF files I van see on my disk.
The UDN2981A.DSN worked OK when I ran the simulator thanks hippy. I even replaced the 2981 with a 2982 and it gives me the same error "Cannot find model file UDN2981.MD " I have even deleted the 2981 from the project library. I have reloaded the program as well. Funny thing is it works on my laptop at work.
Ok yesterday I ran the circuit you gave me hippy and it worked but my circuit still gave the problem. I sunstituted your UN2981 for mine and made a new device from it and it substituted the library one for yours, still gat the same fault. Today...no fault??? Buggered if I know but thanks for your help.
Models are cached within a design file. So even if you rebuild the model externally, if it is already cached in your existing design the new build will not be referenced (the cached model in the file will still be used).
You can change this behaviour from Design>Edit Design Properties menu (uncheck the cache model files option).
If you start again with a brand new design this will always reference the new build.