This error suggests that you have completed the form to say that the annual turnover is less than the £85k limit but the accounting dates entered are not for a full 12 months.

HMRC calculate the amounts pro-rated across a 12 month period and so if the calculation works out for the short period calculated over 12 months would be more than the limit then you cannot complete the short section of the trade pages. You will have to complete in full the Capital Allowances on page 3 and then the trading income on pages 4 and 5 of the partnership tax return.