PHP not accepting single quotes?

All of a sudden, code that has worked for weeks will throw a syntax error on single quotes.

For example

$dueshtml .= '>'. $value .'</option>' . "\n"; 
Copy code

now throws a parse error, and it executed perfectly before. Changing the single quotes to double quotes and escaping any double quotes in literal text allows the line to pass, but I have no burning desire to go though 675 lines of code to convert all of them.

The single quote is indeed ascii 39.

Any suggestions as to why?