I have a very strange problem with my N900. I use it a LOT with fbreader to read ebooks and I have it set up to scroll one page on a finger tap. Now there is one spot on the screen where my finger falls naturally and I think about 90% of all my taps fall in that area. Recently I noticed some finger taps in that area do not register anymore.

Here's where it gets interesting. First, finger tapping anywhere else on the screen works on the first try. Second, once the problem occurs, repeated finger taps in that spot do not register. However tapping anywhere else on the screen works, and tapping again in the problem area also registers. Third, stylus tapping the problem area works every time.

So I tested the screen with the sketch app. I could draw continuous lines, interrupted lines, dots, circles both with my finger and the stylus anywhere on the screen, and every single input registered including the problem area.

Now if other apps had a problem, or the stylus did not register, I may think the resistive layer is developing a problem. But it's limited to fbreader, and only developed fairly recently.

Any ideas? My N900 is running kernel-power47 overclocked to 750Mhz, the latest CSSU, and many apps from extras-devel. Under these circumstances, I would understand some crashes, but the N900 is rock solid with great performance and battery life, except for the wonky finger tap input in fbreader...

fbreader? What is that app for? Is it heavy on the CPU?
I conclude that its because of undervolting the CPU.
In my experience and experimentation, Running multiple apps at the same time causes more CPU load.
Well an idiot knows that too, but, if undervolted, CPU is starved, so working on full load reducees the performance of the frequency causing, in your case, a non responsive touchscreen.
Try cranking up the voltage, see if it works.

FBreader is an ebook reader, and besides loading a book, it's probably the least CPU intensive app out there. All it needs to do is scroll to the next page in a text file when you tap the screen or press a key.

The problem occurs only within fbreader, regardless of how many apps I am running at once. I can multitask between fbreader, opera, media box and only fbreader is affected. And as I said, sketch shows the resistive layer to work in all areas.

What I think may be happening is the resistive layer is getting slightly less responsive in that particular area. There is one setting in fbreader called Movement Tolerance, with 2 options: finger or stylus. If I select stylus but use my finger, the problem is replicated all over the screen.

But I am still hoping there is a bug within fbreader, and that my N900 is fine.

as you said, in certain areas the resistive layer is not that sensitive and with screen protector even worth I think...with the MyPaint program you can check better.
No one can do a settings entry for calibrating the tapping sensitivity?

I'd chalk it up to a FBReader glitch. I don't have that problem, but in the same mode, I'll have it scroll *up* if I'm about 1 finger's width above the bottom of the screen, in both portrait and landscape modes. Hitting the bottom edge of the screen works, but that spot just does the wrong thing.
Who knows why.

Thanks for the replies guys. So in other words, I'm screwed. It's either a minor hardware problem that is not worth spending good money to fix, or a software bug that will never get fixed. Fbreader development has stalled for the N900, last release was months ago.