Getting following error trying to install latest K2 version

Notice: Use of undefined constant K2_JVERSION - assumed 'K2_JVERSION' in /home/......../public_html/administrator/components/com_k2/k2.php on line 20

Fatal error: Class 'K2HelperHTML' not found in /home/......../public_html/administrator/components/com_k2/k2.php on line 77

I have Joomla Version 3.3.3

I had read these forums and confirmed that I had no k2 databases or no previous k2 installations.

This seems to be an issue. I've been having the same issue with 3.3.3 as well as the previous version. Downloading the latest dev build has the same problem, too.

I just tried "Install from the Web" inside Joomla's Extension Manager and I was able to install it successfully.

The first message is a notice, not an actual error.
The second one is telling you that the installation failed.

I dl'ed 3.3.3 and I was able to install both 2.6.8 and the Dev version.

One of those things that mysteriously resolved itself - or else I sat and tweaked so much that I would never recall what it was that fixed it. Probably the latter.