6965 - The entry must be 10 numeric characters, but not 1111111111, 2222222222, 3333333333, 4444444444, 5555555555, 6666666666, 7777777777, 8888888888, 9999999999. Please check. – Partner Details. ABS-33

Absolute Tax Online Filing Errors SA100, SA800, SA900  

This suggests you have entered on the Partnership statement the UTR number for one of the individual partners which is not in the correct format.

When filing online the UTR numbers entered for the partnership as well as the individual partners have to be in the correct HMRC format and need to be valid numbers. You will not be able to file online with a dummy number.