Ringing BLF dials extension twice

[Novais]

I have a small office with 8 phones, all of which ring when a call comes in. All of the phones have the other extensions displayed in the DSS keys and they work great, can dial the extension, can see when the other extension is on the phone etc. When there is a call incoming and the extensions are ringing thats when it creates a problem. If the BLF key is showing the extensions ringing and you press the BLF key to call the extension it dials the extension number twice (ie. 10011001) and says that "your call cannot be completed as dialed" message from the telco provider. If the extensions are not ringing then it doesn't do that, it dials the extension number once (ie. 1001). Any suggestions?