After migrating my site from my local computer to my remote host ( I use Host Gator) with WP Move, suddenly I was locked out of the wordpress admin.
The error I was getting is
"You do not have sufficient permissions to access this page."
In phpMyAdmin, I noticed something strange. I found table records of the suffix used in front of each table, usually "wp_" by default, located in about 8 places in the database. The case of the characters wasn't consistent. Because its hard for me to explain, I'll give an example. To make things simple here, if I had used the default "wp_" as a suffix, I would have found instances of those three characters in some cases as "Wp_", sometimes, "wP_".. very strange.
I thought the entries might be case sensitive so I went ahead and made the name all the same on every instance. Once I got to the capabilties "wp_capabilities", I was able to logon again!
But then, I noticed i had no administrative privileges. So the next thing I found out by comparing with another wordpress install was that somehow my capabilities had been downgraded to "subscriber". I simply copied and pasted the value of "wp_capabilities" from another install which had the same amount of users (1) and the same priviliges.
And thats it. It worked for me in this case and I don't know if this could work for you but its worth the try :)