Use 16 bpp with GRASS

I use Linux as client to link a server for using grass4.1.
I have a problem to run d.mon under 16bpp X window, it have
Error Message that seems it can't find graphic device. Why?
It don't have this problem when it is under 8 bpp.

I use S3 video card, add 'X -bpp 16' in file .xserverrc to
run 16 bpp X window.

Thank you.
      
        Der-Johng Sun
        email: r3206009@cc.ntu.edu.tw (Taiwan)

PS.
I have some problems such as below....

GRASS 4.1> d.mon x1
X Error of failed request: BadMatch (invalid parameter attributes)
  Major opcode of failed request: 78 (X_CreateColormap)
  Serial number of failed request: 73
  Current serial number in output stream: 74
Please start graphics monitor <x1>.
Error - Graphics monitor <x1> not running!
Problem selecting x1. Will try once more
Please start graphic monitor <x1>.
Error - Graphics monitor <x1> not running!

Mapset <botany> in Location <TWR>
GRASS 4.1>

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How to solve it? Thank you for your help.

Grass User.
Der-Johng Sun <r3206009@cc.ntu.edu.tw>