A question about snmpset

[Hongjunli]

HI,

I defined a table containing string variable:

stationName  OBJECT-TYPE
    SYNTAX   OCTET STRING (SIZE (0..63))
    MAX-ACCESS  read-write
    STATUS      current
    DESCRIPTION
            "Station name."
    ::= { meshInfoEntry 1 }

I want to change value of is using  command:snmpset -v 2c -c private 
localhost:163 stationName.234 s "tester",but
snmpset showed me the message:
Error in packet.
Reason: wrongLength (The set value has an illegal length from what the agent 
expects)
Failed object: ARROWSPAN-MIB::stationName.234

why ?

Thanks