c475ip "provider registration failed" on wl-530g with wireless laptop

Hi all,

the following is annoying me for a while and i could not find anything which could help me so far.
I have a c475ip which i use to connect me to my voipbuster account. Everything works perfect, no problems whatsoever... until I turn on the wireless internet on my computer (laptop). Then i get on the display of my c47h "provider registration failed" and I can't use the phone.

I have a WL-530g wireless router running for some years now and also with no problems. I have win7 but same problem experienced before on xp.

The strange thing (for me) is that with a laptop wired connection I can use the phone but with wireless on, not.

Things I've tried:
static ip (c475ip)
fixed ports (c475ip)
other wireless channel (router)

I hope somebody has some ideas.
ps latest firmware in all hardware.

Thanks



edit 13 april '10
I've noticed it does not only happen when connencting wireless laptop but with other wireless devices (psp, pda, mobile phone).
I'm starting to think something is wrong with my router settings, but have no idea what it may be!
Please reply with some ideas.