Why do Access Points fail?

I have 12 Senao NL3054CB3 + Deluxe AP/Bridge units. These are used for a wireless internet network for 160 unit apartment complex and were installed in 4/05. 5 of the 12 have been replaced either by the company that installed the network, or by myself. I currently have 3 AP’s that need to be reset almost on a daily basis. I have contacted Engenius, the manufacturer and did not receive any answers as to why the AP’s are failing. Has anyone else experienced this? How did you resolve the issue? Can anyone recommend a replacement AP/Bridge that would be more reliable?

Thanks for any and all help!

Leslie from Davis, CA