It's been a while, but I vaguely remember that the hyperref LaTeX package for making URLs didn't play nicely with certain other packages -- possibly with one of the citation packages.
Sorry I can't be more specific. I definitely have memories of reordering \usepackage{} statements until "it worked"...
1)pstcol has to be loaded before graphicx (I forget the reason but it just does)
2) if I use pdftricks I have to unset the "clipbox" command because it conflicts with the one in adjustbox.
As you say in another comment, given how latex reports errors debugging these can be a Fun time.