Hello, on the last night of bowling, the last place team's # 4 bowler left a 10 pin in the fifth frame, the number 5 man shot and converted the spare. The opposing team is protesting. The game was finished before i was notifed. Please help, is that frame not counted, is the game forfieted, who gets the win and what about total pinfall. Thank you for help.

I would call the rules department on this one.  I can honestly say I have never heard of anyone having the "balls" to do this.  The only rule I can think of that would cover this would be improper conduct, but it doesn't address this situation.

This is definitely a strange situation. The rules department would be the ones to contact. I would say the frame should at least be an open. Possibly that frame could be counted as a zero, maybe even the whole game by that bowler or possibly both bowlers being forfeited and a zero for one or both for that game. 

 A question to ask before going through with the whole process though. Will this spare make a difference in the games  won/lost by the protesting team?

 My first reaction would be to declare Bowler #4's game forfeited.  According to rule 103b:

When a team and/or individual is found to be ineligible under league or USBC rules, the
game shall be forfeited unless there is a decision to declare the game null and void. In the
latter case, a decision shall also be made as to whether the game shall be rebowled.

Bowler #5 was ineligible to shoot at Bowler #4's spare.  Assuming that Bowler #5's action was deliberate it would be illogical to declare the game null and void, so the only remaining option would be forfeiture.  If it was indeed accidental (which seems unlikely), the spare could have been reset and shot at by Bowler #4 under rule 8:

If an individual bowls out of turn does the delivery count?

No, according to Rule 8, Item d, a dead ball would be declared and the correct bowler is then required
to continue play.

Rule 110c covers total pinfall:

If a team has to forfeit because an ineligible player is used, what happens to the scores
bowled?

An ineligible player’s score becomes zero, and the game(s) is (are) not included in their average. The
team’s score for the forfeited game(s) is (are) also zero. However, the scores bowled by the eligible players
are counted toward their averages and any individual prizes.

The best thing to do would be to call the rules department and let them have fun with this.

Assuming your facts are as described here...rules were broken.  However, you said that this pertained to the last place team, on the the last night of bowling...did this action cause the last place team to achieve victory which thrusted them into the 2nd from last place?

In the business world there is something called the concept of materiality.  If this action caused a material change in the standings, then something should be done.  If the team still ended up in last place, you could persue the issue, but why bother?