Dlink DSL-G604T, DWL-G122 intermittent problems

I am using a Dlink DSL-G604T adsl modem / wireless router. Downstairs I
have a DWL-G122 adapter. First time I set it all up it worked fine.

Next day the adapter's SSID is set to default (instead of the network's
name). Then it worked OK when I fixed this.

This morning it now is asking for a network key. I have not supplied
this before. Do I have to? Why does it do something different every
day?

(signal strength is fine, running XP Prof SP1, security=WPA)

TIA!!!!