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Why doesn't Quantity[] and related functions work for me?

I'm a new user of MMA ver. 10.3.0 Home Edition. I'm trying to learn how to use Units, but it's not working. For example

In[47]:= UnitConvert[Quantity[12, "Meters"/"Seconds"], "Miles"/"Hours"]

Out[47]= UnitConvert[
 QuantityUnits`Private`ToQuantity[
  QuantityUnits`Private`UnknownQuantity[12, ("Meters")/(
   "Seconds")]], ("Miles")/("Hours")]

If I load the Units` package I get the answer I seek:

In[48]:= << Units`

Convert[12  Meter/Second, Mile/Hour]

Out[49]= (37500 Mile)/(1397 Hour)

But starting with ver 9 I shouldn't have had to do that. Any ideas about what's going on?
POSTED BY: Victor Bloomfield
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I often see this problem where units stop working but I have not been able to produce a sequence of commands to reproduce it. However, I have found this commands fixes the issue:

<<QuantityUnitsLoader`

This does not prevent the issue from hapening again in the future but at least fixes it when it happens.
POSTED BY: Gustavo Delfino
Dana DeLouis
Dana DeLouis
Posted 9 years ago
POSTED BY: Dana DeLouis
POSTED BY: Victor Bloomfield
Dana DeLouis
Dana DeLouis
Posted 9 years ago

Just a comment. It's a know issue with Mac Computers since about 10.2 Wolfram told me they are aware of the issue. On a Mac, commands that access "Entity" values from the web also do not work. (Especially accessing Geo' Function. The solution was to reset the Paclet data a few times, and reboot the computer before it would work. It took a while to get it reset on the Mac so it would access the web data correctly.

Just some additional versions...

UnitConvert[Quantity[12, "Meters/Second"], "Miles/Hour"]
Quantity[37500/1397, Miles/Hours]

UnitConvert[Quantity[12, "Meters/Second"], "mph"]
Quantity[37500/1397, Miles/Hours]
POSTED BY: Dana DeLouis

It is probably worth clarifying that this is presumably a sporadic issue--I have never encountered it (Mac installation) and the various folks that I work with who are using a similar installation have not encountered it. As in all cases where something is not working that clearly should work, it's best to contact Wolfram technical support to get the inside track as Dana DeLouis did.

POSTED BY: David Reiss

"Any port in a storm." I'm glad it's working now!
POSTED BY: David Reiss

In fact, I just checked by trying to load Units, and got a "Cannot open "Units`" $Failed result. So whatever I did earlier seems to have provoked a proper upgrade of the installation.
POSTED BY: Victor Bloomfield

For some reason, the old behavior of the Units package no longer persists after I did what I described. Convert[ ] no longer is recognized as a function, but UnitConvert[ ] now is. So I think that the automatic(?) upload from the Wolfram site, triggered by the restart after addition to the init.m file, updated the program properly.
POSTED BY: Victor Bloomfield
POSTED BY: Victor Bloomfield
POSTED BY: David Reiss

Actually I see now that you were getting as a result the Private context expression -- my mistake. ;-)

My comment about not using the Needs["Units`"] package still holds, but there is something wrong with your setup which a bona fide Wolfram employee may comment on. One thing to try is to execute 

RebuildPacletData[]

as well as restart Mathematica.

Sorry for the confusion!
POSTED BY: David Reiss
POSTED BY: David Reiss

That seems to have done the trick. Thanks.
POSTED BY: Victor Bloomfield
POSTED BY: Wojciech Artichowicz
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