I received the above message every time I was trying to compile any files. What I can do to fix it?
Delete the simulation data from the active library.
Make a new design in Active-HDL and then try to compile it.
Check in your design if anywhere any signal is not assigned a default value. Check the default assigned values in the if condition. For ex. Instead of "if (clear) then", write "if (clear='1')".
If the above does not help please reinstall Active-HDL.