This seems to a problem with a certificate from Apple that expired yesterday. This macworld article has the gist:
http://www.macworld.com/article/3004937/os-x/apple-flub-leaves-users-confused-over-damaged-apps.html
So, if you are running the Mac App Store version of GarageSale and are still having this issue, restarting should fixing it.
If you are running a copy of GarageSale downloaded from our website and unlocked using your serial number, you shouldn’t be affected by this problem at all.
However, if you originally purchased GarageSale from the Mac App Store, and switched to the website version of GarageSale, you are in trouble now. GarageSale can no longer validate the receipt file from your Mac App Store purchase as a stand-in for your license and will fail to load.
There are several ways to fix this, but none of them is easy. Please read through all approaches and decide wich one is the best for you. Make sure you have a recent backup of your Mac before attempting any of them.
Variant A: You already own a license for GarageSale 6
- quit GarageSale
- delete the file “AppStore.rcpt” from Library/Application Support/GarageSale
- restart GarageSale and enter your license
Variant B: You don’t have a license key for GS 6 yet, but your are willing to buy one because it’s the easiest way out:
- same as Variant A, but you need your credit card ready
Variant C: Switching back to the Mac App Store version
- make sure you have a current backup of your Mac
- additionally place a copy of the folder Library/Application Support/GarageSale on your Desktop (that’s easier than retrieving it from your Time Machine backup)
- locate your GarageSale application, delete it and empty the trash
- in the Mac App Store, go to the “Purchased” tab and re-download GarageSale
- start GarageSale, if you are lucky all your data is already there and you can stop reading here
- if your data is not there, continue reading
- quit GarageSale
- open this folder in your home directory
Library/Containers/com.iwascoding.garagesale/Data/Library/Application Support/GarageSale
- now copy all the items from the copy of your original GarageSale folder (which you created in step 2 on the Desktop) into folder opened in step 8
- start GarageSale and verify your data is there
- There’s no step eleven!
Hope this helps. Let us know how it goes.