monitor displays "input not supported" message in an otherwise working installation

I installed ubuntu 12.04 yesterday. In the grub-menu I can choose kernel 3.2.0-29 and 2.6.32-41. If I choose 2.6 everything works fine, but choosing 3.2 causes the monitor to show an error message "Input Not Supported" on the screen. In both cases all programs seem to work perfectly, but 3.2 has an extra feature: a gray 4 cm x 12 cm message box moving around the screen in front of other windows. And the picture in 2.6 seems to be a bit sharper.
System Settings -> Displays shows correcty that the resolution is 1280x1024 in both cases. In 3.2 it also shows correctly that the monitor is a 19-inch acer, but in 2.6 the monitor is a Laptop.
lspci shows "VGA compatible controller: NVIDIA Corporation GF119 [GeForce GT 520] (rev a1)" in both cases.
When I choose 3.2 the resolution of the startup screen seems to be higher. At least the "ubuntu" and the five dots are larger in 2.6.
The resolution is perhaps 800x600 during the grub-menu. When I choose 3.2.0 in recovery mode, the resolution changes during start up scripts and the error box appears. In 2.6.32 recovery mode the resolution does not change.
The grub version is 1.5 and the display manager is lightdm.
Earlier I had probably ubuntu 11.10 and kernel 2.6 with no problems.

Any hints?