Hi PPMRam. I had this error as well over the last week or so. My issue turned out to be a migration issue with the workflow. Did you recently change a workflow step and then migrate to a different environment? Remember that changing steps in the workflow almost always trigger errors like this. Another place to check might be the request type if you changed the associated workflow for that request type. Just a couple places to start looking.
Can you isolate the issue to only a particular Request Type ? if you reproduce the error, what is the error in the log files? do you see something like java.lang.IndexOutOfBoundsException: Index: x, Size: x ?
As EngPlan mentioned, this could be caused by changes in the workflow steps, fields, or validations at workbench level, after there are existing request in the system using those entities.