While trying to E-File FPS you will have no employees' listed for a selected pay period in the situations mentioned,

• You would have already completed FPS successfully for that selected pay period and trying to E-File for the same pay period. You can confirm this by viewing the E-filing Status and Certificates under the Reports section.
• You would have wrongly selected the pay period and tried to E-File FPS for the current period.
• You would have not updated the YTD for the particular employees'.