Yes, I beleive you do require a different IOS (a "T" version);
Routers: Cisco IOS Software Release 12.4(3)T and later for NM-AIR-WLC6-K9(=), and Cisco IOS Software Release 12.4(15)T or later for on Cisco NME-AIR-WLC8-K9(=) & NME-AIR-WLC12-K9(=)
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