OpenOCD / Yagarto / Eclipse / GDB / JTAG Problem

Hi,

I use a full Yagarto Toolchain (OpenOCD, arm-elf-gcc, arm-elf-gdb,
Eclipse) in conjunction with the Amontec JTAGKey (JTAG device). I want
to debug code on an Olimex LPC-P2129 Evaluation Board.

Things work fine as long as I don't try to step over blocks of code and
as long as I keep my debug sessions short. However, whenever I try to
step over large blocks of code (like a long while-loop) or whenever I
let the target run for long sections of code, the whole thing hangs up,
that is, OpenOCD quits with an error message, JTAGKey hangs up
completely and must be restarted by unplugging from USB and arm-elf-gdb
also crashes.

Has anyone any idea what might go wrong?

I use a standard configuration file for OpenOCD and a standard GDB
configuration script at startup. JTAG Speed is 2 (6 MHz / (2 + 1) = 2
MHz. Clock Speed is 14,745,600 Hz.