FRM-10102: Cannot attach PL/SQL library APPCORE

Problem :: FRM-10102: Cannot attach PL/SQL library APPCORE. This library attachment will be lost if the module is saved

Solution  :: Need to add FORMS_PATH  in registry of windows. 

Press Win R to open windows Run and put regedit to edit the windows registry.

Search for FORMS_PATH 

Include custom Forms and PLLs path in this variable.