Comment on Stallion SEO Theme Support by WordPress SEO Theme Author.
There’s nothing in Stallion that might cause something like that. Have you tried switching back to the theme you had running before Stallion, does it work?
Check your permalinks settings under
Settings > Permalinks
.htaccess file rules, make sure they match the ones on the permalinks page.
Did you make any other changes between installing Stallion and checking a post and realising the posts aren’t loading correctly?
Highly unlikely Stallion is the cause.
Edit: I see you solved the problem within an hour or so of this comment, was it the permalinks/.htaccess rules?
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