Question: "Bad range arguments" in plot3d

I have to calculate and plot the volume of a cicloid where a equals 27. Now, the assisstant gave us the supposed code to work with, as most were having trouble with it. Here it is:

with(plots)

plot3d(27*(t-sin(t)),sqrt((27*(1-cos(t)))^2)*cos(s),sqrt((27*(1-cos(t)))^2)*sin(s),t=0..2*Pi,s=0..2*Pi);

However, this gives me the following error when trying to execute:

Error, (in plot3d) bad range arguments: ((27-27*cos(t))^2)^(1/2)*cos(s), ((27-27*cos(t))^2)^(1/2)*sin(s)

 Now, only I and those I have sent this code verbatim to have experienced this error, while others in the class who typed it themselves didn't encounter this problem. I think there might be an assigned variable unaccounted for, but then again I did make sure to use restart.  I am using Maple 16, for the record.