Your formula returns 4 characters. =LEFT(M8,FIND(" ",M8)-1) will return the characters up to the first space (and excluding the space).
TRIM(N8) would also remove trailing spaces if you plan to keep your formula as it was. In that case =VLOOKUP(TRIM(N8),Lookups!J5:L2772,3,FALSE) would also work, but this is less likely to throw an error:
(=VLOOKUP(LEFT(M8,FIND(" ",M8)-1),'Lookups'!J5:L2772,3,0))