I really dislike problems where we're supposed to guess how partner went wrong. At the table, I always assume partner has his bid, and would have made the correct bid earlier in the auction. I do the same here. I'm left with a 0=4=6=3. Pass.
I must be missing something; if it was MPs, I'd probably X, but since it's IMPs, I trot out RKC (yes, it has to be RKC and not Quant, etc.), and I'm taking either the dead-sure 5♠/NT, the pretty-damn-sure 6♠/NT, or the might-be ...