Memory card error in android mobile

Android experts please,
I have a smart phone with android 1.5.
A separate 2 GB memory card is installed with 70% free space on the memory card.
I have configured the DEFAULT downloading to this memory card instead of phone memory.
From the very first day, I am facing the problem that whenever I try to down load a program, I receive the error that there is not enough memory to download this program, although the file / program is in kbs.
However, if I try to transfer any file via the usb cable or Blue tooth, the files are easily loaded on the memory card without any error. Is this an Android issue? Or something to do with the configuration I made?
Regards,
savoly
