Run problem in Nios II

The associated Nios II system library project for the application project is referencing a non-existent SOPC Builder system file.

Please select the application project, and select Project->Properties->Associated System Library to choose a different system library project. Alternatively, copy your SOPC Builder system file to the location specified below.

i am running DE2_NET project in DE2 Demonstration. while in Nios this error occurs please help :(