Session upgrade to v9.2.1 failures

Going back to open a few old sessions that were in C1 v8.x (April 2015) I'm asked to upgrade to v9.2.1 & contantly getting 'Database connection FAILED'. Any ideas anyone? The only solution I've found so far is to trash everything to do with C1 from that folders session & start again from scratch. Which is complete pain in the wotsit as all & any adjustments are totally lost.
MacPro 2013 model: 3.5/ghz 6 core: 64Gb RAM: Running Yosemite