Well, what i said about attributes not being critical is not accurate enought, i will try to explain a bit for the record
You need to take a look at this table, contains all the attributes known
XMBML Structure - PS3 Developer wiki
Some of them are just for the eyecandy, are the ones related with "what is displayed in screen".... like the icon, the title of the icon, icon_notation, icon_rsc, etc... info, info_rsc, title, title_rsc etc... this are the ones used everywhere (in xmbm+ and webman) for displaying images and texts, and are not mandatory
Some of the others are making some "special" effects that are associated with some function, but are not well known, like bar_action (for the progress bar i guess), or lbl_half (note this one is used in mysis cfw settings... we had an small discussion of what this attribute does, and i still not sure but the fact is it solved a problem in mysis cfw settings)
But this kind of attributes are not used in xmbm+ or webman... so i dont think the error comes from here