Strange Error In IE5.5,6.0

[bob@nospam.dotdotdot.org]

i'm currently revamping my site and decided to use this excellent menu feature. it works fine running under mozilla, but through ie5.5,6.0 i keep getting the same error

line 31, char 275, invalid argument

any ideas about what could be causing this. my site is http://new.losblaugrana.com if you want to take a look. its a football site for barcelona.