You cannot include a comment in an output expression while working with server side scripts. For example, the first line that follows will work, but the second line will not, because it begins with <%=. It is advisable to separate the comments if such a need arise:
<% x= x +1 'this increments x. This script will not fail. %>
<%= arReturnValue 'this prints the variable varReturnValue. This script will fail. %>

However, if you break the second line so that comment and the output expression is separated, then there is no error.
‘This prints the variable varReturnValue. This script will not fail.
<%= varReturnValue %>