I repair computers and have come across this exact same scanner problem only in the last 2 months on 3 different computers which I havent been able to find a solution for, even after googling for numerous hours, tonns of others are having this problem too and i cant find any real solution. 

So far its happened to me on two older brother all-in-one fax/printer/copier/scanners's and one older HP office jet 7100 series (cant remember models of brother machines), all newish computers running xp pro sp3, all amd systems too.  the exact error message when trying to access the scanner thru my computer is "The scanning software could not be found, or your scanner is not connected,  Please make sure your scanner and your scanning software are properly installed." 

I have been down all troubleshooting paths, reinstalling software/drivers, downloading updated software/drivers, problem will not go away, even clean install of xp pro sp3 on one of the amd system running a brother machine.  all other functions work fine, prints no problems, copies no problems, faxes no problems, just cant scan from pc, get above error message. 

The most recent problem, the office jet 7100 series, the customer could scan previously but not now all of a sudden.  im assuming its something to do with windows updates, sp3 compatibility issues maybe?  going to check renetly applied updates to system running the office jet.  if that failes to show the source of problem, its going to be a real time waster to sort out, going to try clean install of xp pro sp2 on new test hdd in one of systems, set up scanner make sure it works and apply updates one by one checking scanner each time till i hit the culprit. 

I have seen a patch for this problem on the hp website but not for any of the models i have worked with.