It is not clear why you are trying to use things in the
QuantityUnits`Private`
context like
QuantityUnits`Private`ToQuantity
That is certainly not the correct way to proceed--almost always avoid using undocumented functions and always avoid using anything in a Private context. For your particular example the correct syntax is
UnitConvert[Quantity[12, ("Meters")/("Seconds")], ("Miles")/("Hours")]
And I would suggest removing Needs["Units`"] from the initi.m file as it will load a legacy pacage that was superceeded by internal Mathematica functionality as of version 9. See
http://reference.wolfram.com/language/Compatibility/tutorial/Units.html