Most likely, you have either 0 units entered for the service line, or you entered fractional units and the payer you are submitting to does not allow fractional units.
How to fix
The units are entered on the add / edit session form. You will want to open the edit session form for the sessions on the claim and edit the units (under the Service Codes section on the edit session form). For your convenience, if you are on the EDI rejection page in Therabill you can open up the edit session forms by clicking the dates of service on the right hand side of the error page (under Claim Information). Once you have changed the units, make sure you save the session by clicking the Save & Done button at the bottom of the edit session form.
If you are on the EDI rejection page and you have already updated the units, you can then click the Resubmit Electronically button at the top of the EDI rejection page to resubmit the claim with the updated information.