Natural Frequency Extraction in conjunction with UMAT in ABAQUS

Hi,

We are using the user subroutine UMAT in ABAQUS for varying the material properties in a thin plate. For any static analysis this subroutine is working perfectly fine. However, while using UMAT during natural frequency extraction, ABAQUS is not completing the analysis and is giving a very vague following error message in the log file:

Abaqus Error: The executable C:\Program Files\SIMULIA\Abaqus\6.9-3\exec\standard.exe
aborted with system error code 5.
Please check the .dat, .msg, and .sta files for error messages if the files
exist. If there are no error messages and you cannot resolve the problem,
please run the command "abaqus job=support information=support" to report and
save your system information. Use the same command to run Abaqus that you
used when the problem occurred. Please contact your local Abaqus support
office and send them the input file, the file support.log which you just
created, the executable name, and the error code.
Abaqus/Analysis exited with errors

There are no error messages in .dat, .msg or .sta files. Sadly, this error message is not helping in finding the cause of the problem.

Are we missing something, like initial conditions, to be defined in UMAT? If somebody has used UMAT during eigenfrequency analysis, kindly suggest.

Thank you

Vaibhav Yadav