Compiler Warning (level 1) C4560
'argument' : non-constant default arguments unavailable when importing function
This warning results when you use a non-constant value as an argument to a .NET function that is called when you #using its module. .NET metadata can only represent constants as values for default arguments to functions. The default argument would still work as expected when #using is not used.
Remove the default argument or find a constant to use as a default instead.