Check if there have some Macro's enabled in the users excel.
try below workaround -
Try adding a Workbook_Open event procedure, and set the Enabled property of the AddIn class to True to force the AddIn to load. I'm not sure if that will work or not, but it's probably worth a shot.
I have the exact same problem with one user, but with Office 2010. Did you find a solution? Have the user installed Adobe Acrobat and SAP Business Explorer?
Best regards, Robert
This has been logged in as an ER Bug 16753437 : EXCEL IS NOT RETAINING SMARTVIEW ADD-IN WHEN YOU OPEN IT FROM WINDOWS EXPLORER
Disable the preview pane before you select any Office documents (including Word, Excel and PowerPoint). Note that once the program is running in preview, you will have to kill it in Task Manager before you can use SmartView again OR open Excel from the Start menu and open the file by File > Open or similar.