[antlr-interest] Help with this grammar?

[Charlie Hubbard]

I'm having trouble with the following piece of a grammar:

ruleOptions
    : LPAREN
    ( keyword:IDENT (COLON keywordParam)? SEMICOLON )* RPAREN
    ;

keywordParam returns [ String param = "" ] { StringBuffer buf = new
StringBuffer(); }
    : (letter:~SEMICOLON { buf.append( letter ); } )* { param =
buf.toString(); }
    ;

This portion recognizes one or more keyword parameter combinations. 
Each keyword is optionally followed by a section of parameters. 
Really it is only a single parameter, but that parameter could contain
more than one option.  The keyword-parameter sequence is ended by a
semi-colon.  So here is an example:

( message: "Hi, there this is a paramter of message keyword";
classtype: blah; rev: 6;)

The following parser works, but it is failing on some characters I
didn't expect.  I'm currently getting the following error:

exception: filename:17:93: unexpected char: '>'

Here is the line it's having trouble with:

msg:"EXPLOIT delegate proxy overflow"; dsize:>1000; 

the '>' character is not recogized by that grammar.  Why?  I thought
the use of ~SEMICOLON would recognized everything, but ';'.

I'm new to ANTLR, but I'm beginning to get the hang of it.  But I'm
still getting hung up on little things like this.

Thanks
Charlie