I'm not sure what is happening but it still works for me running 10.3.1 under OS X.

What does happen sometimes is the input aliases somehow get locked into the User's init.m file; the aliases persist even when the package is not loaded. It happens rarely and might be connected to a Mathematica crash when the package is open. Fixing this is clunky; I get into the Option Inspector under "Global Preferences", open "Editing Options" => InputAliases and then delete all of the package's input aliases.

I don't know if this is your problem but the InputAliases might have become corrupted.

Terrence, thanks again for a quick and very useful response. I've deleted the old versions of your palette, downloaded the new one and installed it. BTW, "installing" a new palette without first removing the old one from the UserBaseDirectory does not overwrite the old file.

I just installed your interesting palette (with the same mistake as Ben Rodanski...). Your palette writes "Nonoseconds" in the cell expression. Shouldn't it be "Nanoseconds"? It evaluates correcly as Nanoseconds, though.

Ben, the Wolfram units system does not simplify as a default. The package and shortcuts do not change the behavior of this units system; it just allows for easier and prettier input. To simplify, use the UnitSimplify function. The palette has a //UnitSimplify button and with the shortcuts installed you can get that with the shortcut esc us esc.

Raymond, I'm not sure if there are any Wolfram NSolve issues with units but your posted second expression had only two equations, where your first expression had three. It gave no solution but didn't crash for me. Adding the third expression does give the result in SI, which is odd. The only way I could convert to lbs. and in. was to follow it with: /. (x_ -> y_) :> (x -> UnitConvert[y, "Imperial"])

just installed, tried it on a simple shear stress problem and having problems;

without units, I get a solution

Clear[aa, \[Tau]1, \[Tau]2, t1, t2, T]
t1 = .2; t2 = .3; T = 50000;
NSolve[{aa == (3.5 - t2/2)*(4 - t1) + .5 \[Pi]*(2 - 
       t1/2)^2, \[Tau]1 == T/(2 aa t1), \[Tau]2 == 
   T/(2 aa t2)}, {aa, \[Tau]1, \[Tau]2}]

but when I add the units, as soon as divide T by aa the solution crashes

Clear[aa, \[Tau]1, \[Tau]2, t1, t2, T]
t1 = .2 Quantity["Inches"]; t2 = .3 Quantity["Inches"]; T = 
 50000 Quantity[("PoundsForce")/("Inches")^2];
NSolve[{aa == (3.5 Quantity["Inches"] - t2/2)*(4 Quantity["Inches"] - 
       t1) + .5 \[Pi]*(2 Quantity["Inches"] - t1/2)^2, \[Tau]1 == 
   T/(2 aa)}, {aa, \[Tau]1, \[Tau]2}]

two problems:

1. my units are in inches, yet the result is in m^2, how can I keep my original units??
2. how can I prevent the crash???