I tried to do it according to the instructions in the help menu, however PSE 11 does not even recognize the file format.
How did you transfer the pictures and catalog to the new PC ? The recommended way is to do a full backup on the old PC, and a restore on the new one.
The restore process should first restore the picture files, then convert the catalog to the new PSE11 format.
The problem is different if you install PSE11 on the same old computer, you don't have to move files, only convert to the old format catalog.