Jonathan Heaney, in bug #262862 discovered a problem with mac80211 being unable to handle APs with hidden ESSIDs. The problem occurs only in 2.6.28 kernels and is fixed in 2.6.29. Reproducible: Always Steps to Reproduce:
I sent a mail to the linux-wireless mailing list about this bug. You can find the thread here: http://marc.info/?l=linux-wireless&m=124059633132688&w=2
No apparent fix for 2.6.28, workaround is to use 2.6.29 which we'll work towards stable