Tag pages do not show

problem:

• When I request a “tag” page e.g. /tag/whatever no tag page shows up only the frontpage. This also seems to be the case with categories

what did i do

• I have moved this blog from single site to my WP3 Multisite setup (#21)

What Did I try already

• The other 20 moved weblogs work OK so it is not “generic” or .htacess or wpconfig
• I have tried other themes like 2010 : the same problem
• Just to be sure I flushed the permalinks
• “if(is_tag()) { echo “”; } else { echo “”; }” always show “no tag”… in other words the page itself does not think it is a tag page
• the table structures and database contents for terms, etc… look ok
• i have a template page “tag.php” with in it “hello tag”, this one does not show
• the backend looks completely ok: tags show with posts etc..
  the tags DO appear under the posts

Current Hypothesis

• hmmm could it be the multi domain plugin something?
  do i have to start debugging
• https://phpxref.ftwr.co.uk/wordpress/nav.html?wp-admin/options-permalink.php.source.html#l62 word for word?

any leads to give a brain spark? must be something stupid