@Thomas Richard 

I installed 2021.1 update und tried again. Now it works correct.

@TechnicalSupport 

I just tried this example again on my computer (Windows 10, Maple 2021.0).
Now I get sometimes the error and sometimes not. Once the error disappeared it doesnt appear until I start Maple new.

I get the error, if I open Maple, press "new file" and paste the 2 lines.  (separately )

And

I do not get this error, if I press File->New->WorksheetMode

In the beginning for me, it looked like it depends on the way, how I create a new document.

But maybe it depends on the way how I paste the example.
Copy the 2 lines in an text editor:
with(Student:-Calculus1);
ShowSolution(Int(sin(x)^2, x));
And then copy each line separately into Maple

@acer 

No this posting is not from me.

Thank you for trying out with Maple 2017. As it works on your computer, it seems to be a version or configuration problem. 

If I run the sample with Maple 2019, the last command "fsolve" is not evaluated. Just compare the last line of my and your output.

I did edit the question to reduce the problem on this point.
 

Download CoolProp_01.mw

I'm using UltraEdit. This editor allows to convert the file from ASCII to UTF8.

When I do this, it works in Maple 2017.

Independend from the mpl-file, Maple 2017 has difficulties to distinguish "ü" from "ü":

> h1:="hüstel";
                         h1 := "hüstel"
> length(h1);
                               7
> h2:=StringTools:-Substitute(h1, "ü","ü");
                      h2 := "hüstel"
> length(h2);
                               11
> fd := fopen(terminal, WRITE):
> fprintf(fd,h1):
hüstel
> fprintf(fd,h2):
hüstel
 

While writing this comment, I found something strange:

If I copy the command with the result into this editor, I get the following:

h1:="hüstel";
                         h1 := "hstel"
If I copy only the result  into this editor, I get the following:

h1 := "hüstel"

Found a solution for this. If the special character is coded with HTML, it is read correct.

Example

test:=proc()
print("hüstel");
end proc:

I read the file with

> read("test.mpl");
> test()

"hüstel"