xrandr custom resolution problem

[Fill23]

I have a problem with setting up custom resolution. I want 1280x960 70mHz,i'm using it in winXP, but ubuntu fails to detect it automaticly. And when i try to add it manually i get an error.
My monitor: Samsung SyncMaster 755dfx, it's crt.
My video card: Radeon HD 3650 AGP.
Here what i'm trying to do:

xrandr --newmode "1280x960" 121,000 1280 1368 1504 1728 960 961 964 999 -hsync +vsync

Mode line was extracted from windows program PowerStrip, but i also tried lines generated by gtf and cvt. Now when i'm type 'xrandr' i get this:

Screen 0: minimum 320 x 200, current 1280 x 1024, maximum 1280 x 1280
DFP1 disconnected (normal left inverted right x axis y axis)
DFP2 disconnected (normal left inverted right x axis y axis)
CRT1 connected 1280x1024+0+0 (normal left inverted right x axis y axis) 306mm x 230mm
   1280x1024      75.0*+   75.0* 
   1152x864       75.0     75.0  
   1280x720       60.0  
   1024x768       85.0     85.0     75.0     70.1     70.1     60.0     43.5  
   800x600        85.1     72.2     75.0     75.0     70.0     60.3     60.3     56.2     56.2  
   720x480        60.0  
   640x480        85.0     75.0     72.8     75.0     60.0  
   640x432        60.0  
   640x400        75.1     59.9  
   512x384        60.0     74.9  
   400x300        75.0     60.7  
   320x240        75.6     60.0  
   320x200        75.5     60.1  
CRT2 disconnected (normal left inverted right x axis y axis)
TV disconnected (normal left inverted right x axis y axis)
COMPONENT_VIDEO disconnected (normal left inverted right x axis y axis)
  1280x960 (0xb7)  121.0MHz
        h: width  1280 start 1368 end 1504 total 1728 skew    0 clock   70.0KHz
        v: height  960 start  961 end  964 total  999           clock   70.1Hz

but 'xrandr --addmode CRT1 1280x960' produces an error:

fill@mainframe:~$ xrandr --addmode CRT1 1280x960
X Error of failed request:  BadMatch (invalid parameter attributes)
  Major opcode of failed request:  156 (RANDR)
  Minor opcode of failed request:  18 ()
  Serial number of failed request:  31
  Current serial number in output stream:  32

Anyone knows what is going wrong here? Or what am i doing wrong.

[Fill23]

Installed fresh default Ubuntu Karmic (was on CrunchBang - Ubuntu Jaunty ) and now all works.
Still dunno what was causing this.
But now i have a slowdown preformance. Jst yeasterday i was able to play 720p mkv video with out laggs and now it freezes every second.
As far as i get it the problem in the ATI driver wich is different from 9.04. If somebody could give me a hint where to look, i would realy apreciate that.