John,The error is because the + sign in between your keywords is missing in the links to pages 2 and higher.
For example, search for gardening supplies - the first page is returned properly, but the link to other pages includes the search term as gardening supplies instead of gardening+supplies.
Did you make any changes to the program and/or template that would cause that? I'm away from home right now, so I can't look at the code, but that's where to start.
Jeff