thanks to all for help ... it turned out that gem-0.84 was compiling with the libparticle from gem-0.81 (in another directory). i have no idea how this happened. i deleted the old directory and started over, now all is well.
thanks again, b
Probably you have a second, non compatible libparticle somewher in /usr/lib ... you can look at the link line of gem, which should show a -lparticle flag
Guenter