As you said, not much to go on…
Check the IPSEC Phase 2 lifetime. They must match on both ends.
Beware that not all vendors describe the lifetime in the same units (seconds, minutes or hours), so be sure that you are comparing apples to apples.
The phase2 lifetime can also be specified in amount of data transferred. Again, they must match, but don't use time and amount lifetimes at the same time, that gets confusing.