HI could you try the below steps
1. Open Microsoft Dynamics NAV Administration from All Programs
2. Select the NAV Service which you are using now
3. Click Edit at bottom
4. Increase Max. Upload Size from 30 to 50.
5. Click Save at bottom
6. Restart the Service.
OR
Change the value for below property in CustomSettings file
<add key="MaxUploadSize" value="20"></add>
and restart the instance