Ah, it's pretty well known that SAMI sucks because it corrupts mods, mostly car mods.
Use the tutorial provided by NotYouHaha, that way you can see if it's SAMI or the mod itself.
Trivia Warning - XLR8: If you don't know the answer, do not even reply to the question. Thanks.
@ Question: It's the NRG500
My Question: Name all stadium challenges?
Also, if you don't want to spend 5 minutes rebuilding an archive, use this IMG editor. You can even drag the files from the .zip to there and click Save (it's instant and it works), it's express.
Trust me!
How do you know it didn't finish? It says "archive rebuilt in (X) seconds", so that means it's already done. Seconds vary in your PC's current performance and HDD activity.