Search your harddrive for "MSDeploy.exe"....and see how many different versions you have.
Then experiment with setting the "ToolPath"
<MSDeploy
ToolPath="C:\OneOfTheFoldersWithMsDeployExeInIt"
Verb="sync"
Source="@(DeploySource)"
Destination="@(DeployDestination)"
AllowUntrusted="true"
/>