It is possible that the reason the error message displays on the expense run validation detail screen is that the process has been run already.
To confirm, check the following.
In Back Office, click CoreExpense.
Click Tools, then click Process Logs.
Search for the expense group and current run number to see the expense process that has been carried out.
The following processes should appear on the process log:
Submitted EXP4000 - This is displayed when the generate payment claims is run.
Validation Complete - This is displayed when the validation run process is run.
Paypath Generated - This is displayed after running the create paypath data process.
SP Timesheets Passed - Optional can only be seen if used by the organization.
Complete Update - This is displayed when the complete cheque update is run.
Ledger INT - This is displayed when the Interface processing is run.
Update Submitted - This is displayed after the validation process is run.
If any of the processes are missing, you would need to complete this in order to close the expense run.