YahooACE V1.0.0.569 (Yahoo Chat Client) by Brian Meeks like YTunnel and YTK and its Vista Compatible.
For Download:

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If you have a problem with the software, try to complete its file system and registers the file system in the folder. you can get the system files here, register files for xp user click here, register files for vista user click here, unregister files click here. If you are still having problems with the program try to contact with the programmers to the website / forum where programmers follow.