Is R2012 pointed to that central location? Or did you never centrally locate them? If you did nothing special in the old version of AutoCAD then simply loading R2012 would not mean the program will find them.
Please elaborate, share with everyone your geography of file and folder locations etc.
What is SSMAUTOOPEN variable set to in 2012? SSLOCATE variable? SSFOUND variable? How do these settings compare to the older version?
Did you already delete the old AutoCAD version you where using?