actually the official ROM is bulky and take too much space in useless programs and this results in short space available thats why i always suggest usin gCOOKED ROM without useless stuff in it and it gives u more space in device memory may be 130 MB or more
for now pls reset ur device like this
while phone is OFF
press SEND and END both buttons while pressing them press Start button on top until u see a screen to format the device that will erase all data warning
after this kindly update ur ROM from here
http://www.samsungmobile.com/support/omnia/index.jspand in future kindly when u install programs install them in ur other big partition never install stuff in DEVICE MEMORY install in storage memory when asked during installation
it might be a software bug and will be removed in latest update kindly go to the above link feed ur phone details and downlaod the drivers and ROM update for ur device and then simply connect ur phone thru usb cable provided and then follow the instructions u can ask me for more detailed instructions i am expert in this
i would suggest using a COOKED ROM with only useful stuff and leaving the rest with more free space u can asl me where to get this ROM for Omnia