mvision hd 300 scrambled channel

hi,has anyone had any problems with the dtt side of this receiver,the words :scrambled channel: appear on the dtt channels intermittently,when this happens it overrides the dtt picture and sound making viewing unwatchable,changing dtt channel will sometimes clear the message and normal viewing is restored,however sometimes when the words ;scramble channel; appear on screen no amount of channel changing will clear it,powering off the receiver will clear it for some time,but it will return.
satellite reception is perfect and when dtt is working the picture is very good with no picture freezing or break up,i did a factory reset and deleted all channels and retuned but the dreaded message returned again,and when the message comes on screen it will stay all evening ,anyone any ideas?thanks.