Left brace: '{', is one of the special characters that needs to be escaped using a back slash: '\{'. { is used to introduce a counted pattern as in: '{10}' - match the character or group to the left ten times. If { isn't followed by a pattern matching '\d+(?:,\d+)?' then the '{' needs to be escaped.

It may be that the version of Perl you were using previously was older than you are using now and the handling for that case has changed.