How to resolve ERROR: FRM-18108 while compiling the form in R12

FRM-18108: Failed to load the following objects.

Source Module:APPSTAND
  Source Object: STANDARD_PC_AND_VA
Source Module:APPSTAND
  Source Object: STANDARD_TOOLBAR
Source Module:APPSTAND
  Source Object: STANDARD_CALENDAR
Compiling package specification APP_CUSTOM...
   No compilation errors.

We get this error when we try to compile a form in Oracle Application.

Source Module:APPSTAND Source Object: Differs.

The above errors occur when the referenced forms either cannot be found, or cannot be opened.
In the above example, the problem is with APPSTAND.fmb and INVSTAND.fmb.
This will occur if FORMS_PATH has not been set, and $AU_TOP/forms/US has not been added as described earlier.

Open New Terminal
Export the Forms Path as
$export FORMS_PATH=$AU_TOP/forms/US:$FORMS_PATH

See that you have appropriate permission on $AU_TOP/forms/US/APPSTAND.fmb.

Now compile the form again.

Hope its successful.....

If the problem is still persist then :

a)  Ensure you can open the referenced forms in the builder
b) If all else fails, use OS tracing to determine why the referenced forms cannot be found or opened.