Excel 2013 - Nested IF(ISERROR(SEARCH not 'seeing' final statement

I'm struggling to see why the below isn't working for the final statement:

=IF(ISERROR(SEARCH("Investment Commentary",E73)), IF(ISERROR(SEARCH("Quarterly Update",E73)),"Quarterly Update"),"Investment Commentary")

So in Column C is my formula, and Column E contains text I'm searching. My original formula has 12 of these and they all work....except for the last one. I thought perhaps I'd hit a limit, but for some reason it refuses to 'see' the final IF statement and simply returns FALSE.

Any help would be much appreciated! Thanks Michael