Why are IP conflicts occuring days after a wireless access point and bridge are installed?

Two weeks ago I installed an Access Point and Wireless Bridge to supply connectivity to our office down the hall.  Ten days later our entire network was taken down by IP address conflicts on all windows systems.  I had the AP running in "AP Only" mode, not handing out DHCP addresses, and the bridge was hooked up to catalyst 2900 switch, which goes to the patch panel.  Everything was running fine for those 10 days.

I disconnected the AP from the network and the IP conflicts vanished and our main office connectivity went back to normal.  I've since tried swapping out the AP with another model and the same error occurred, taking down the network.

The configuration in the other office isn't out the ordinary, just a few Cisco 7960 IP phones, and a few desktops/laptops.  Nothing in that room could possibly be handing out DHCP leases.  We only have 1 subnet and the DHCP server shows that there are 98 leases still available.

The bridge and AP are running in infrastructure mode, the bridge does not have the gateway or DNS defined as it is just acting as a repeater for the main office's access point.  Nobody in the main office associates with the access point either, it's dedicated to providing connectivity to the remote office only.  Both the AP and bridge have the latest firmware, and the configuration has been triple checked for possible conflicts.

What could possibly be causing the conflicts?
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IP conflicts often happen if the ports on switches and NIC's aren't correctly matched. If you have managed switches and you have their ports set to a fixed mode, like 100MB/Full Duplex, and the other device connected to that port has another setting, IP conflicts occur. The best way to stop this is to set all ports to autonegotiate.

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The AP could also have an address that's from the assignment pool. That's why it works for a while - that address is (or was, rather) unassigned by the DHCP server; As soon as DHCP issues the AP's address to another device, the conflicts appear.
mcokely01844Author Commented:
Sure enough a DLINK 5 port switch was installed by someone who didn't check the configuration.  We pulled that out today and the IP conflicts seized immediately.  Many kudos!
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