Because your tag name is not well-formed. XML seems to require that every tag starts with an alphanumeric alphabetic character, underscore or colon.
Maybe you can make XML::Simple more lenient, but I recommend changing your datastructure instead.
Update: Changed wrong "alphanumeric" for "alphabetic"
In reply to Re: XML::Simple cannot parse Simple XML file
by Corion
in thread XML::Simple cannot parse Simple XML file
by jeanluca
| For: | Use: | ||
| & | & | ||
| < | < | ||
| > | > | ||
| [ | [ | ||
| ] | ] |