When my backups come in I'm getting my one of my backup QB's playing center, WR's playing Guard and Tackle. My settings at Oline is @ 90 with no rules.

Im still getting my 3rd string QB giving up sacks. My o-line has a depth of 4 and 5 deep.

Is this preseason or regular season? Your OL backups aren't also first string in other positions, are they? I'm wondering if you just have a more complicated situation like the kickers getting benched because one is #1 as kickoffs and the other is #1 as field goals, them both getting benched and therefore no kickers remain available.

It's in pre-season with MFN-1.
I'm also getting backup WR's playing center in the 2nd half. Oline fatigue is set at 80.
I do have backup centers playing other Oline spots as well.

Remember that when the starters are pulled, the #1 player for each position is benched. If they exist elsewhere on the depth chart, they will be removed from there as well. So if you have overlap in that manner, you can run out of depth chart.

gotcha.

Don't know if it's possible or not but if there is a way to prevent this sort of substitution it would be more realistic. Having the ai put a TE at tackle or even a Dlineman on the Oline would be a better option than QB's, RB's, CB's or WR's at C, G or T.