Carbonite worked for 3 days, backed up files OK then stopped at 28% of initial backup.

This issue has now been escalated to 2nd line and I am awaiting a response.

In the meantime, if you have a problem with Carbonite installing then it is worth looking at the logs it creates which can be found at the following location (in Windows XP)

c:\Documents and Settings\All Users\Application Data\Carbonite\Carbonite Backup

NB: you need to show hidden files, because the Application Data folder is hidden.