1050 - Property '%s' must be of type <%s> (found <%s>).

Description
The property of a Function was of a type other than that which is expected by the Function.
Example
Config:
Library( 'lib' ) { .LibrarianOutput = true }
Output:
c:\Test\fbuild.bff(1):(1) FASTBuild Error #1050 - Library() - Property '.LibrarianOutput' must be of type <String> (found <Bool>). Library( 'lib' ) ^ \--here
Fix:
Library( 'lib' ) { .LibrarianOutput = 'output/mylib.lib' }