You're not crossposting you're multiposting, there is a difference.
Crossposting is fine as long as you don't overdo it and as long as you
crosspost to relevant groups.
For an example of why multiposting is bad go in the other newsgroups
where you posted to see possible solutions. If you had crossposted
instead of multiposting the answers from respondents in other groups
would also appear here. And of course you won't see this reply in the
other groups where you multiposted. This not only wastes your time,
going from one group to the other to read replies to your question, but
it also wastes the time of the respondents as they may be answering
questions that we already answered in another group. It can also reduce
the quality of the help that you receive as one of the strengths of peer
help groups is that the answers can be reviewed by other readers and
they can add supplementary information to the advice already given or
point out potential problems or mistakes with the suggested fix.
Finally, many of the helpers will not bother with your post if they see
that it was multiposted, they don't want to put their effort into giving
answers which might have already been suggested and discussed in other
groups.
http://www.blakjak.demon.co.uk/mul_crss.htm
Multiposting vs Crossposting
John