Try to go on compiler options of the package remove from the path the "../fpc" press ok and compile will error, open again the compiler options reinsert the "../fpc" press ok and compile again is supposed to work then install, sometimes that procedure worked with me.
Also give preference to put the package on lazarus dir/components.
I've already be able to install on a mac, but after a download the svn version and imprudently override the already instaled version they stop do compile. Now i don't been able to install Indy anyway. Wich is very weard because i've already tried to remove all the installation files of fpc and lazarus and get back that enviroment of before but i wasn't able in anyway i've tried.
By now isn't urgent to me to make work on a mac, the windows project is the one that i'm working on. But in the future i'll have to again. If you or anybody find out how, please send to us the tips for.