I recently needed to upgrade phpMyAdmin and ran into the following 2 gotchas.
First I tried to upgrade to 3.x and was getting the following error.
unknown character set ‘utf8’
This was due to the fact that I was trying to connect to a mysql version 4.x so I had to download the latest version compatible with mysql server 4.x which is 2.x
The second gotcha was I set my blowfish secret to 64 characters which caused an error in the apache logs below:
PHP Catchable fatal error: mcrypt_encrypt()
This was due to the fact that the blowfish secret cannot be longer than 56 characters.
Denise's Tech Blog 