Cannot transfer purchases from iPhone to iTunes on my Mac

Hi,

I've an iPhone 4 running OS 4.2 and I recently purchased music via the iTunes app for the first time.
When I tried to transfer the tracks across from my iPhone to iTunes (v 10.1.1) I got an error message saying:

"Attempting to copy to the disk "Macintosh HD" failed.
You do not have enough access privileges for this operation."

There was no error number.

I have tried using 'transfer purchases' in the File drop down Tab and I have tried highlighting the iPhone in devices and using the option there but still no joy.

I have removed the tick from manually manage music... no change.
I have enabled my iTunes media folder as a shared folder. no change
I did the same with my hard drive.
I enabled file sharing between the iPhone and my Mac still nothing.

If anyone can help it would be greatly appreciated.