snmpset notWritable (That object does not support modification)

[daniloreiss]

Hi I'm trying to write a new agent snmp. I start with a file written in ASN.1 and then I execute:
./configure --with-mib-modules = "mymib"
the ASN.1 code is as follows:

mymib OBJECT-TYPE
SYNTAX DisplayString
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"My mib"
:: = {1} myoid

when I start the snmpd process and try to run the snmpset command, I get the following error:

snmpset -v2c -c myprivate localhost mymib.0 s "test"
Error in packet.
Reason: notWritable (That object does not support modification)
Failed object: myoid :: mymib.0

with the command:
snmpset -v2c -c myprivate localhost sysName.0 s "test"
the command works properly

if I change "SYNTAX String Display" to "SYNTAX Integer32" and execute:

snmpset -v2c -c myprivate localhost mymib.0 i "10"

it works properly

can someone help me?
Thank you all