I read with interest the various opinions about downloading MSTS.
I am ready to re-install it, Mr. deJong has some pertinent points .
The Administrator in Win 8.1 is a royal pain, running with administrator does NOT always work in 8.1
It raises a few questions for me however.
Do I download everything with C:\trainsimulator, and omit program files altogether?
Will I get rid of that everlasting message "cannot open output file", as nobody seems to have an answer
for that, not even on the internet.
Find this forum very educational, hope I get some answers.
Greetings from Canada,  Anthony.

I really don't get what you're saying, installing MSTS directly under C:\ is always a good idea.

Sorry, my mistake, I will explain better.
It has been suggested in this forum that downloading MSTS to just" C:\MSTS" rather than
C:\Programfiles (x86)Microsoft Games etc.etc. you will have less Administrator interference.
And just may be I am not understanding it right.
And that is what I am saying!

SIGNED,      Anthony.

If installed the right way, it shouldn't be necessary, although it might make things easier for you.

I can't really say if it gets rid of the "cannot open output file" message, just try it and see if it does. 

But if your account has full rights to your program files folder you can install msts to it without problems.