WPA2 TKIP and AES

I have this setting on the WL300g and it works with computers that can handle AES and with a Nokia E90 and an older computer that, seemingly, cannot.

However I posted this finding to a Nokia forum and someone there claims that the E90 can use AES.

Could anyone throw any light on this? I would be interested also to know if the security is AES when a computer that is able to use it accesses the wireless network at the same time as one that cannot. Does the whole network only work with TKIP in that case, or are individual devices able to negotiate different protocols, so that one may be using TKIP and aonther AES?

With many thanks in advance.
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pqb