Summary:
There could be cases when there are timesheets waiting on approval however one of the approvers may have left the company and is disabled in the application. In these cases the timesheet is stalled waiting for the disabled approver to approve.

Resolution:
The issue can be resolved by enabling the approver for the time being and the administrators can set themselves as substitute to him/her. Log into Web TimeSheet as substitute user for that approver and approve the required timesheets.