Hello Jack and welcome to Vista Forums.
Yes, you are correct that sometimes changing the user account name can cause problems with it. Usually with older programs that are installed though. The spaces should not be an issue in the name.
Do you have a C:\Users\Jack and Nancy
folder or is it also C:\Users\'
If it's the later, then it sound like the account was originally name '
instead. The only way to fix
that is to create a new administrator account with the name you want and delete the old one from within the new one afterwards.
Hope this helps,