I have a Toshiba TG01 on Vodafone Pay as you Go. I'm trying to change the call forwarding settings - so that unanswered calls go to voicemail after 30 seconds (rather than 15 seconds). When I try to apply these settings, I get the following error message;

"Cannot save your changes to the network. Try changing settings later, or disconnect data connection and try again."

Does anyone know how to overcome this?

Not sure if this is relevant but the phone was originally tied to Orange UK before I bought it. I use it otherwise with Vodafone PAYG without any issue otherwise.