It turns out that the uninstaller for i-mscp does not always work. At times it just fails, leaving an unusable system, on top of which, a new version of i-mscp does not allow to be installed. If this happened to you, follow the following steps to completely remove i-mscp and allow it to get installed again.

First, login to your phpmyadmin and remove all databases (Can also be done manually):

Access pma at,
User: Root
Password: yourmysql root password

If you forgot the password, you need to reset it

Delete all existing databases with a name imscp or roundcube in it.

Now, you need to delete all directories used by i-mscp:

find / -iname imscp -exec rm -rf {} \;
rm -rf /etc/apache2
apt-get remove apache2

Now reinstall imscp.

tar jxf imscp-1.1.0-rc3.tar.bz2
cd imscp-1.1.0-rc3