I have a multiple selection variable named fruitVariable, and it had following choices:
apple
orange
dragon fruit

 I passed the value of fruitVariable to a MSBuild property and got the following error:
  MSB1006: property is no valid
  Switch: orange
 <path>/MSBuild.exe /nologo /t:test "/property:fruitProp=apple,orange, dragon fruit" .\build.xml

 However, I ran following MSBuild command line manually, it was successfully
 <path>/MSBuild.exe /nologo /t:test /property:fruitProp="apple,orange, dragon fruit" .\build.xml

 Looks MSbuild plugin added the double quotes at a wrong location.

 Please look into it when you have earliest chance.

 Thanks,
ptrinh