ptrace is restricted on hardened linux to child processes. this effectively disallows gdb --pid
unfortunately mainstream distros (ubuntu 10.10) go for hardened now.
creator should preload some code into the debugee that does something like http://websvn.kde.org/trunk/KDE/kdelibs/kdeui/util/kcrash.cpp?r1=1206730&r2=1206729&pathrev=1206730
note that the code is wrong. You must not use undefined ptrace request values. Howeber, It is possibly they did this to work around missaligned kernel header vs kernel version packages in ubuntu.