"Constants are always private to the rest of the script; they cannot be local to a function nor public to child scripts."
Which can be interpreted both ways - if a Constant is "private to the rest of the script" this could mean "private to the script and viewable by any function within" or "private to the rest of the script (which is what it says), needing to be declared inside a function". Ok it then says "cannot be local to a function", but guess that's my fault for not reading the whole paragraph
The problem may be that the const function doesn't like the inclusion of variables like your MyVar1. I wasn't able to concantenate a variable in the constant declaration, but was able to reference the constants from within a function. Perhaps you can create a function to accomplish what you want and include the function in other scripts that you want to reference it???
This one worked for me:
Const MyConst1 = "here is a string "
Const MyConst2 = " more stuff"