RN2483 433MHz problems

I'm trying to use the RN2483 on 433MHz - but its not playing ball. All I seem to get is the "invalid_param" message back when I try to set frequency. Setting frequency in the 868MHz band works fine. Here is what I get:

COMMAND                                    RESPONSE
sys factoryRESET                           RN2483 0.9.5 Mar 24 2015 14:15:33
mac get band                               868
radio get freq                             868100000
radio set freq 868500000                   ok
radio get freq                             868500000
mac reset 433                              ok
mac get band                               433
radio get freq                             433300000
radio set freq 434000000                   invalid_param
radio set freq 433300000                   invalid_param
radio set freq 434500000                   invalid_param

Any clues?