Redmine

Hi
I'm currently administrating redmine server in our organization.
currently we are facing some intermittend issue while loginh new issue(Defects), we are getting the below error message

Internal error
An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.
If you are the Redmine administrator, check your log files for details about the error.

I can confirm that we haven't made any changes related to the redmine infrastructure recently and we hanen't applyed any patches to the server. The only thing we could see is on a project we cant edit/delete a defect in the system, we have trird to delete that particular defect and getting the error message, *in error *.
we beleave this can be deleted via backend, we are using MYSQL in the backend, but not sure what exactly the process which need to perform this. Can you please guid or advise me what are the steps involve?