Wireless Bridging Dlink APs and Cisco

A(2000)--------->B(2100)---------->C(2000)
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Cisco
2600
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Internet

AP in A is DWL-2000 in "Wireless bridge" mode
AP in B is DWL-2100 in "Multipoint bridge" mode
AP in C is DWL-2000 in "Wireless bridge" mode

AP in B is connected to Cisco2600 on Int fa 0/0
Int fa 0/0 has two IP addresses (one Primary, one Secondary)
Primary address is default gateway for A
Secondary address is default gateway for C

Cisco2600 is connected to DSL via Int fa 0/1

The issue we are having is PCs both locations (A and C) are pingable from the Cisco2600, but not at the same time. If a PC in either location is active, the Cisco can ping that particular LAN, but not the other. Has anyone ever encountered this issue? Is there something in the configuration of the 2100AP that is causing this issue?