Problem with Multiple OR Statements in Formula

Hey All,

I'm having issues with a formula. I've narrowed it down to the 3rd IF statement in the VLOOKUP section, specifically the OR statement.

Here is the formula:

=IF(ISERROR(VLOOKUP(O8,$L$35:$P$45,IF(N8="R",3,IF(N8="M",4,IF(N8=OR("A","B","C","D","E","F","G","H","J"),5,"UNKNOWN"))))),"-",VLOOKUP(O8,$L$35:$P$45,IF(N8="R",3,IF(N8="M",4,IF(N8=OR("A","B","C","D","E","F","G","H","J"),5,"UNKNOWN")))))

The problem lies with N8, which is a letter grabbed from another string. If I change this to "R" or "M", it works fine. If I use any of the other letters ("A"-"J"), it resolves to "-", which is the ISERROR resolution.

Can someone take a look and tell me what I'm doing wrong? AFAIK, I can nest a bunch of variable in an OR statement, so I'm not sure what's wrong.

Thanks