IMC switch config backup fail when stacked switch

[SuporteZL]

I have a problem with IMC only when I try backup config in switches stacked and specific models.

Error mesage:

SNMP Set operation failed.

1. Check that the SNMP parameters are correct. With SNMPv3 adopted, the username, authentication password, privacy password and privacy mode for the device and the iMC should be the same. 
2. Check the MIB style (Execute the display mib-style command. If the MIB style is displayed as new, but it displays that the node sending the Set request is 2011 after packet capturing, synchronize the device. Check the MIB style again. If the MIB style is still inconsistent, execute the mib-style [ new | compatible ] command, and then restart the device.). 
3. Error code such as no such name may occur for the Set operation. You need to capture packets to analyze whether such error occurs in the response received by the device. 
4. Device busy, please retry later.

But I test the snmp and telnet credentials with success.

The switches model: 3COM 4500, 5500G

I had others switches the same model and firmware version, but non-stacked, the backup works successfully.

I had the switch model HP3600-48 POE stacked, the backup works successfully.

Thanks for any help