Yes, Sgn(Null) will return error, so do conversion functions. I wonder whether should I send some patches to fix the conversion functions.

As for Sgn(Null), I don't know how describe this error, I mean, I can't match the error_const_value between wine and windows document. For example, when Err.number = 458, it is described as DISP_E_BADVERTYPE in wine while in windows document it is Variable uses an Automation type not supported in VBScript  (http://msdn.microsoft.com/en-us/library/xe43cc8d(v=vs.84).aspx)

I have found that when Sgn(Null) is called, Err.number = 94, this error is described as Invalid use of Null, but I can't find the correspond description in wine/include/winerror.h.