Cannot install updates of OS X 10.6.3 or any other software

Thanks for your reply Niel. It at least set me thinking and indirectly led to a solution. Before approaching my ISP (the thought of spending 20 mins on hold before getting to an advisor who will probably tell me I need yet another new modem doesn't much appeal!) I decided to try a few things. I connected my Macbook directly to my modem with a USB cable, giving up my wireless connection and bypassing my Airport express. I was then able to download most of the indicated software updates and install them when I did them one by one rather than all at once. I still was unable to update the system software (which was the original point of the exercise) but somewhere along the way - I can't now remember how or the exact sequence of events - I became aware that that Apple Software Update application needed updating too (although Software Update itself didn't tell me this). Once I had done this I was able to download and install the system 10.6.8 Combo update. It was all a bit of a mission and took me far longer than such a supposedly straightforward operation rightly should but I got there in the end. I wish I could remember how I discovered that Software Update needed updating because that could be an important piece of the jigsaw for anyone else witha similar problem who is reading this. Maybe if in doubt do it anyway (it's available from the Apple Downloads section (http://support.apple.com/downloads/).

Niel, I have another question regarding the message I got when I repaired permissions: "Warning: SUID file "System/Library/CoreServices/Remote Maagement/ARDAgent.app/Contents/MacOS/ARDAgent" has been modified and will not be repaired." Do you know what the impllications of this are and should I be worried??

Thanks. Francis

That's reassuring, thank you Klaus.