Unable to ring extensions

[Arismac]

I have recently purchased a T46G (line 50) and three W52P (lines 51,52,53) with base station. The T46G is connected to the router with Cat 5. The W52P are cordless, of course. My telephone service provider is Telecube in Australia.

When I try to call any of the extensions from the T46G two phones ring about once out of every three attempts, the third not at all. When the extensions do not ring the Power Indicator LED flashes quickly. If the extension is ringing the Power Indicator does not flash. All three W52P can call the T46G.

The W52P that does not ring at all sometimes displays "BUSY HERE" but the extension is not busy. This W52P that does not ring at all is physically located quite close (5m) to the router and base station.

The display on the T46G show small white crosses on red backgrounds alongside the softkeys which I press to try and call the W52P's. These crosses are a permanent fixture but can not find what they indicate.

Help please.

Thanks, Mac