I have the same problem in Visual Studio 2012, please try the following:
- add a new empty workflow
- place a single AssemblyInfo activity there
- fill in its AssemblyCompany - set it egz. to "aaa" (including double quotes)
Now blue exclamation mark icon appears on the right side of property editor with tooltip: "The left-hand side of an assignment must be a variable, property or indexer". The same problem occurs in other properties. In real workflow for TFS builder the
tooltip message is "Invalid L-value expression" as nanderto wrote.