Seen this many times.
Update your video drivers.
Should go away.

I have seen it too, but we never could get a reliable case to redo it.
There seems to be a relation to opengl drivers, but also with good drivers I heard it happens in cases...

Does scaling down window help? Not run fullscreen?
(moving to opengl tracker)

Moved from Blender 2.5 Bug Tracker to OpenGL errors

Thankyou Ton for replying.

I've tried everything (including change the screen resolution, color to 16bit and back to 32 bit, resizing the window). Nothing worked. I've noticed the same issue at work with the desktop I use there. I can get its techinical specification tomorrow and post here for comparison.

Blender 2.49 works perfectly with both machines.

Did you save a startup.blend with settings? Try "file -> factory settings" if that solves it. Don't use the 'fullscreen' button in top of header.
You can also just save a default empty .blend and attach here, then I check it too.

Hi Ton. I did what you said and the problem is not yeat solved. As promised, here is my PC (at work) configuration on wich the same issue occurs.

CPU: Pentium Dual Core E5400 2.7GHz
RAM: 2GB
OS: Windows Vista Business - Service Pack 1
GFX: Intel G33/G31 Express Chipset Family ~ 287MB
Driver: Intel Corp 7.14.10.1255
Resolution: 1024 x 1280 (32bit 60Hz)

the startup.blend file is attached attached. Also, a new user preferences window snapshot taken after reload the factory settings.

even if I run blender in XP compatible mode and with administator privileges, the problem remains.

Thankyou.

Your startup file loads fine here.
BTW: on your screenshot I noticed the the preferences is a full-sized window. How do you open it, try top menu File -> User prefs

Ok. I tried some different steps based on your previous comment and it worked. When I open the user screen preferences using the top menu File -> user prefs or by pressing the short cut keys (Ctrl Alt U), the problem occurs (no matter if it is in full screen mode or not). On the other hand, if I select user prefs from the icon in any window (3D window for instance), the user prefs window appear perfectly (readable).

I mean, when the user prefs is reached throught menu file or shortcut keys, the user prefs window is popped up as a new window with no readable contents. So the problem occurs only when the user prefs is a pop-up window.

You can see the user prefs working on new attached image (not a pop-up window). Only this way the user prefs is readable in both machines no matter if Blender is in full screen mode or windowed mode.

Thankyou Ton for guiding my to solution.

OK: that pins down the error to a bad state in opengl context when a 2nd window is being opened... in that case any 2nd window would be bad?
Just try ctrl+alt+w

Yes. Any 2nd window is bad. See attached (ctrl+alt+w pressed). Is that a local problem (in both machines) or something to fix in Blender?

There's something in initializing opengl for a 2nd window that behaves differently for Intel graphics cards... unfortunately, none of the 70-80 active devs has this issue. We need someone with a similar system to check the code what's missing...

I have this problem in 2.63a all of a sudden so I switched to 2.64a, it doesn't happen there. I tried loading the 2.64 startup.blend in 2.63 but still error. Have had this happen in
the 2.5 series over the years.