Add in's dissappear

[stephme55]

Hello. I downloaded the xlam file for power pivot utilities. I put it in the add in folder and then went to excel add ins and chose it, and then it appeared in my ribbon. However, when I reopen excel it's not there, even though the add in shows up as selected.

[stephme55]

I opened another file, went to browse and reselected file. It says a file already exists here and then I chose to replace and now it shows up on the ribbon. However, when I reopen the file, the add in dissapears. Why is this?