Core issue
The Port Aggregation Protocol (PAgP) attempts to remove a port not in the spanning tree data structure, causing this error message to be generated.
Resolution
The %SPANTREE-3-PORTDEL_FAILNOTFOUND:9/5 in vlan 10 not found (PAgP_Group_Rx) message indicates that the PAgP attempted to remove a port from the spanning tree for a specified VLAN that was not in the spanning tree data structure for that VLAN.
Typically, another process (like the Dynamic Trunk Protocol [DTP]) may have already removed the port from the spanning tree.
The %SPANTREE-3-PORTDEL_FAILNOTFOUND messages are used for debugging purposes. These messages do not indicate a switch problem and do not affect switching performance.
The %SPANTREE-3-PORTDEL_FAILNOTFOUND messages are not logged unless the default SPANTREE facility logging configuration has been changed. The default logging level for SPANTREE is two.
You can revert the logging level for spantree to two by issuing the set logging level spantree 2 command. This prevents these informational messages from being displayed.
For additional information on error messages, refer to these documents: