I first explained my solution for this problem on Sandvox Support Forum back in September 2008. I have decided to put my written tutorial here. I have removed my screencast video because the information in it was being abused.
It is not uncommon that after updating the application, Sandvox will not be able to publish the site. This is very often a problem caused by Keychain Access which stores the passwords needed by Sandvox to access the Host of the website. I worked this out during the multiple beta testing updates of Sandvox 1.5. I discovered that if I don't quit Sandvox a second time after an update, I don't see the ->Keychain Allow dialog (image link) as mentioned in First Solution:–Step 5 below and 'Publish' fails, even if I re-enter all my FTP settings during this first relaunch period.
First Solution: The 2-seconds Fix
1. I update Sandvox either by installing the automatic update or using Sandvox > Check for Updates...
2. Sandvox downloads the update and I click 'Quit and Relaunch'.
3. Once Sandvox has relaunched, I quit and relaunch Sandvox a second time.
When Sandvox restarts this second time after updating:
4. I click Publish
5. ->The Keychain Access Allow or Deny dialog (image link) comes up
6. I click ->'Always Allow' (image link). Clicking 'Publish' in Sandvox will *hopefully* then works.
If the First Solution doesn't work there is a second solution.
Do not do this if you are new to computers or like to sue if you 'mess up'. You are responsible for what you do.
Second Solution: Proceed with Caution
This solution involves deleting the binary key for Sandvox from Keychain Access. I list various options to the information about how to do this.
Option 1: The Karelia online Help document about this is here:
http://docs.karelia.com/z/Diagnosing_Keychain_Problems.html
Option 2: This is an annotated screengrab I have done, of the Keychain Access 'Get Info' window. The steps needed to remove the "old" binary signatures of Sandvox are numbered.
->Annotated Screengrab of Keychain Access
Option 3: Short screencast covering just the Keychain Access issue. [Removed]