I know this is an old problem but I have not been able to solve it.
I have taken over a site for someone and cannot get the K2 component installed.
Running Ice Theme Community template with JomSocial on Joomla 3.3.3.
I have deleted the tmp folder, cleared and purged cache. Deleted the com_k2 folder in the components directory. There was a table in the DB called k2_attaachements but no others.
It will not allow me to install K2 from the web. I tried installing by uploading the standard and dev packages. Both to no avail.
I tried to "discover" but this did not work. I cannot uninstall because when going to the extension manager and searching for "k2", nothing is returned.
The dev site is at
staging2.youmustlovedogsdating.com 
