Please make sure that the "Zoom" feature is turned off, which is under Preferences app > Accessibility.
The app cannot detect more than 2 fingers at same time when it is turned on.
Please make sure that you are plucking the black area on the bottom of the screen instead of the wooden fretboard.
Sometimes it seems to crash when you don't have enough memory. Please turn off your iPhone by holding power button, and turn it on again. If it still crashes after reboot, try reinstalling the application. For details about reinstalling the application, please read the article from Apple.
You cannot press barre chords by laying your finger because of the limitation in the hardware. Instead, after you put your finger on the fretboard, drag your finger horizontally to the fret.
It sometimes seems to happen when the language preference of the device is not English (e.g. French or German). To show the messages in English, please choose English in your language preference first, and change it back to your language again.
If you still have any problems, please send email to the following address.
If the application is crashing even after rebooting the device, it would be very helpful you send me crash logs located at following places on your computer after you sync it with your device.
Mac OS X: [Home Directory]/Library/Logs/CrashReporter/
Windows XP: C:\Documents and Settings\[User Name]\
Application Data\Apple Computer\Logs\CrashReporter\
Windows Vista: C:\Users\[User Name]\AppData\
In this directory, you will find some files that begin with "PocketGuitar", e.g. PocketGuitar-2008-08-22-213936.crash. Please put these files into a zip archive and send it to me.