15" PB and external monitor

[Samaritan]

Hi all

I'm trying to connect my Powerbook to an external monitor. Its an oem generic 17" tft - my Powerbook reports it as a PV1710.

If I connect with the PB on, its fine. It runs a spanned desktop of its native 1280x1024, or mirrors fine with by PB display.

However, if I try to run the PB in clamshell mode, the monitor say "out of range"

Any ideas?

Ta

Sam