Issue during MIRO - "Enter G/L Account"

Hi,

We are facing an issue during MIRO - "Enter G/L Account"...

Scenario: We had created a Work Order thru ME21N tcode with Account Assignment category 'U' (unknown). Also, maintained the Service tax condition type under Conditions tab. After that, create SES and process MIRO. Here, system asking for G/L Account.....

Please suggest.