At a guess you may be installing a version that was not designed for v5.5 ie Greg Zartmann's contrib which was for v5.6.
I see on contribs.org that someone (forget who it was but have a look) has released an improved version that works OK on v5.5
If that's not the case for you, then the message is saying that another rpm is needed that is not already on your system (ie a parser). This parser issue was answered many months ago on these forums I think it was by Charlie Brady around the time Greg Zartman released his contrib, do a search on Parser (all dates).
Hope this helps
Ray