In my first Population writing one value to excel and in second using that value from Excel, but I am getting error?

Have 2 population in Scenario, in my first Population writing one value to excel and in second using that value from Excel, but I am getting error

Error detected by NeoLoad
Error Code: NL-RUNTIME-02
Message: Internal error occurred playing the request.
Details: java.lang.IllegalStateException: Variable "generated_workorders" does not have values.

Please refer to the documentation for further details and advice

But when i check in excel the data was written correctly in excel