I am using Windows 7. I downloaded the latest daily version to my normal folder and running the .jar like I normally do.
I do not have mafia in any other folder on my computer.
If More info is needed let me know what you would like and I will provide it.
More scratching my head since 15608 works just fine.
I just went here, right clicked (in Firefox) to download and save KoLmafia-15609.jar and it runs just fine on my Windows system. Since you actually saw the word "corrupt" in your error it is most likely that what you downloaded did not download properly. Regardless of the cause, the first step is to download it again
When I ran it from the command prompt from the folder I got:
Error: Unable to access jarfile KoLmafia-r15609.jar.
While I was in the folder I noticed the timestamp on the the file was the same as when I first downloaded. I deleted it and redownloaded again (even though I thought I did already) Worked fine. Must of not saved right for some reason when I first downloaded it.
Problem solved.
Probably should of just waited for 15610 like I was going to do, but thought if the file was indeed corrupt you all should know.