Just adding this to help someone in future:
The company I work for is re-vamping its main site, built on WP, and on which I have a number of pages with multiple loops, customizing with category and Post ID exclusions in the queries, etc. It's a little complicated and so will the changes be to implement.
I started a repeat install (with a different admin name to keep things clear to me which one I was working on!) of the actual site in a subfolder, and uploaded a copy of the database from the real site so I can work on it out of the public eye before doing the changes.
I found that the redirection plugin page in the dashboard was blocked to me with the "you do not have sufficient permissions to view this page" message. Other plugins did not do this.
After a bit of poking around, I realized that I had uploaded the entire database, including the redirects done on the other site. Since you can only redirect URLs of your own site, I am assuming the plugin would not let me have access to them in the "new" site. I didn't want the redirects on the practice site anyway, so for the repeat install I just deactivated the plugin.
Long explanation... but this might help someone have a clue where to look in a similar situation. Other plugins might react the same way.