If Malwarebytes throws up an error and won't launch, just delete these files and folders from Y:\Programs\MalwarebytesPortable:


App
Data
MalwarebytesPortable.exe
MalwarebytesPortable.ini


Then, open MalwarebytesPortable.7z and extract the files to replace the ones you deleted and Malwarebytes should work again.

Just make sure you update the definitions, and exit the app from the Systray. 

Re-open the app with the updated definitions, and you should run a Custom Scan. Find your C:\ drive (It may have a different drive letter assigned to it) and run the scan.