Has anything changed physically in your environment that could be causing radio frequency interference? or have the clients moved further away than normal? I looked up that syslog message and got the following:
Q. What does error message mean: "Packet to client xxxx reached max retries, removing the client"?
A. The Packet to client xxxx reached max retries, removing the client error message means that the AP disassociates the client because the client did not respond to max keep-alive messages sent by the AP. This can be an indication of a bad RF. Configure this command on the AP in order to eliminate this issue and to enable the client to not lose the connection:
packet retries 128 drop-packet
The increase of packet re-tries to 128 with the drop-packet option is a workaround for the bad RF problem. Refer to Configuring the Maximum Data Retries for more information on this command.
Taken from: http://www.cisco.com/en/US/products/hw/wireless/ps4555/products_qanda_item09186a0080094cdc.shtml