iphone camera not found error message

Hi,

I have been connecting my iPhone 4 to My iMac 27" since I bought the iMac (about 1 month ago) and in the last week I have started getting the message "camera not found" every time I connect my iPhone to the iMac using one of the direct usb ports on the back of the iMac.

This is frsutrating and a pain as I want to download photo and for it to work properly.

My iMac OSX is 10.6.7

My iPhone 4 is 4.3.3 build 8j2

Anyone got any ideas how to fix tihs?

Thanks in advance,

Peter from Guildford UK