Once you installed WB 3.1, download the latest version from http://whdload.de/ and then extract the files. Put the file you will find in C directory inside your WB 3.1 C directory and the files in S directory inside WB 3.1 directory and that's all.
This operation is possible only when you load WB 3.1 and not from Ambient due to hdf file. So put the WHDLoad directory inside your "Data" directory and when you start WB 3.1 copy the above mentioned file froms Data to WB.