Core issue
The %SYS-2-SHARED: Attempt to return buffer with sharecount [dec], ptr= [hex] error message indicates that an internal software error has occurred.
SNMP ENGINE SYS-2-SHARED Attempt to return buffer with sharecount 0 which is similar to %SYS-2-SHARED: Attempt to return buffer with sharecount 0, ptr= 41C58C0
This issue is documented in Cisco bug ID CSCef48078.
There is no known impact of this bug on the normal functioning of the switch. It is unlikely that the switch reloads because of this bug. Any other side effects are also unlikely.
Resolution
As a workaround, ensure that there is no Simple Network Management Protocol (SNMP) authentication failure. For example, if the SNMP request is for a community that is not configured on the switch, then these messages get triggered.
Even in the case of authentication failure, SNMP traps for authentication failure are sent to the Network Management System (NMS) as expected.
Cisco recommends to configure the no logging console command if these messages become a nuisance. If the error message is received even after the command is configured, then upgrade to Cisco IOS Software Release 12.2(18)EW2 or later.
Error message
%SYS-2-SHARED
