What are some reasons a TT as prof may be denied tenure in your experience?

[Kron3007]

I think giving any sort of general recommendations without knowing the OP's field and university (ranking, focus on research or not, etc.) might not be helpful. For example, if you are at a university that is really serious about research, they may ask you to bring a CAREER award to get tenure. On the other hand, if at my department they do not give tenure to anyone that publishes more than 1 paper (even if it is a crappy one) per year and probably has more than 10 citations per year, they will have to fire all the assistant professors but one. And as you probably have noticed, I am not even mentioning ANY grant activity. And we claim to be a "research-intensive" department. Of course, we are not, but when I say that people get offended.

I think the one general comment that does apply is to consult with your colleagues and chair to make sure you are on track and have a clear explanation of what is required.  Even within a single department there usually is not a golden set of numbers since there are so many factors.

[teach_write_research]

To take it to a more generalized level, tenure denials happen because of (1) poor communication and (2) lack of support.

That poor communication can manifest on the side of the candidate as a lack of pubs or unsuccessful teaching. It can also manifest on the department and institution side as unclear or changing criteria. The lack of support can be no or minimal service engagement by the candidate or insufficient resources, different priorities etc. from the institution. I'd put financial exigency in that support bin too.