Compiling separates with GPS GPL version (Ada 2005 i think)

["stuart clark" <stuartlclark@hotmail.com>]

i have package spec which declares two visible task. Thye package body
then declares these tasks as separates. i then have the task in
individual files named

common_to_both_1553-io_1553.adb

i have compiled both the package spec and body, however when i try to
compile the separates is get the following;

gnatmake -u -c -u -PC:/GNAT/uatl/uatl_common_lib.gpr
common_to_both_1553-io_1553.adb -d
gcc -c -I- -gnatA "C:\Documents and Settings\stuart\My
Documents\UATL\uatl\common\common_lib\common_to_both_1553-io_1553.adb"
cannot generate code for file common_to_both_1553-io_1553.adb (subunit)
to check subunit for errors, use -gnatc
gnatmake: "c:\documents and settings\stuart\my
documents\uatl\uatl\common\common_lib\common_to_both_1553-io_1553.adb"
compilation error

process exited with status 4


Questions
1) What am i doing wrong???

2) Can i invoke a gnatmake myself in GPS, i tried a GPS shell but it
doesnt recognise the gnatmake command. Is there some way of manually
compiling stuff. At present i am simply doing a SHIFT-F$ to compile the
separate.

Stuart Clark