You have encountered an unexpected error. Please contact the System Administrator for assistance

Issue :

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After applying Patch.R12.HR_PF.B.Delta.6 - Oracle HRMS Release Update Pack 6, We have faced some of the forms library files are not generated successfully. 
While trying to click on any of the HRMS self service link, it shows "You have encountered an unexpected error. Please contact the System Administrator for assistance. 
Click here for exception details "

Soution :

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This issue has produced due to wrong patch application on application tier..

Refer "Multinode patching(blog)" to apply patches in multinode environment.

Because of this Appl1 and Appl2 have oracle forms and library files version mismatch occurs.

Hence I have copied required files from concurrent node and applied all the patches successfully.