When I log on to Windows, I get runner error "invalid backweb application, id 137903", how do i fix this?.

You have downloaded a program that contains spyware or adware. Parts of the spyware or adware has been removed but parts do remain and the program requires the spyware to be installed in order to run, without it you will get the Run Time error. This program runs on startup so you will have to uninstall the program that had the spyware associated with it. Run Msconfig from the Start > Run window and turn off the progam that you downloaded, or uninstall the program. If you still cannot find the program do a search for files that contain the word "Backweb"

Still cannot seen to cure the issue then do this:

Create an account here  first.  Now login, download this program HijackThis1991.exe.It will create a directory folder for you in C\Program files.When you run the progam,check for updates.
Doubleclick HijackThis.exe icon. Press the <Scan> button.Do not scan in safe mode.
DO NOT FIX ANYTHING YET!! Most of the entries found in a HiJackThis scan are programs/files which are REQUIRED for your
computer to operate normally.

Press the <Save Log> button and save into your HJT folder.
The log should automatically open in Notepad.
 

Now start a new thread here http://www.cyberanswers.org/forum/forumdisplay-f_12.html . In it describe your issue as well as copy and paste the hijackthis logfiles contents for one of the experts to view.