I have made a site with a custom theme on the latest version of c5 but i am getting

Fatal error: Call to a member function getVersionID() on a non-object in .../concrete/models/block.php on line 93

This has happened all of a sudden, the site worked fine while developing. I had an index.html file up as a coming soon page so would use index.php to check what the home page looked like as i developed the site. I haven't edited any core files other than my Theme. This error only came up after i took down the index.html page. please help as the site was meant to launch today.