Power Nap doesn't work right in my MBA mid 2011. Anyone knows why?

I just boght a MBA middle 2011 and power nap doesn't work right on it, specially in Mail app, where it downloads only a few mails and the rest of them are downloaded as usual, when recativate my laptop. Does anyone knows why?... i also tried to download the SMC update, but when i try to install it i get the message that my system is not compatible with the update.

Please somebody help me!!

Thanks in adevence!