This error occurs when the Spanning Tree Protocol (STP) debug is on. These messages are cosmetic and occur when you have either bridge groups or VLANs. This is caused by the specific debug spanning tree exception and can be ignored.
This issue is documented in Cisco bug ID CSCdt71887.
Ignore these messages:
Externally found moderate defect: Resolved (R)
Bridge group no free chunk available
The feature these messages refer to (optimized BPDU transmission for switch VLAN spanning trees) is not used by the bridge group.