I appreciate you trying to help me out.
I've double-checked the partner code and it is correct. As I live in Québec there are two partner codes (one for feds, the other prov, and both are 0), and that's what I have entered in the respective boxes.
I actually have a second error message (in addition to the Box 116 and Box 118 issue) which tells me I am not permitted to enter "general business income (loss)" if I have a partner code of 0 and that I should have entered instead "limited partnership income (loss)". Regrettably this error message refers to Box 08 for the partner code but there is no Box 08 on the UFile form (or on the T5013), as partner code goes into Box 002. I do know that if I delete Box 118 and leave it blank all the error messages go away.