I get this kind of error when I forget to escape an '@'
in quotes (like $email = "me@mydomain.com"; )

The error does not occur when I escape the ampersand,
as in $email = "me\@mydomain.com";

Do you have an ampersand in quotes anywhere in your code?

Not sure if that is your problem or not, but...

A monk asked his teacher,
"What did old Masters attain when they entered the ultimate stage?"
"They were like burglars sneaking into a vacant house," the teacher replied.