I am using Windows 7 and have installed Adobe Digital Editions 4. When I try to borrow a book from the library, it says it can't find the program

I am using Windows 7 and have installed Adobe Reader 4, in order to use a Kobo E-Reader.  When I try to "Borrow" the book from the Library, I get a message that it cannot find the program to use to open it.

This problem started about 2 months ago.  Up to that time everything worked well.

Hoping for a solution.

Any answers?