George, the CAS module has not been tested in a long time, so it is possible that there has been an update in the core that has broken it. See how the dateConvert function works in core, and then search the module and see how it is different.
If you fix it, just increment the version number in changelog, changedb, version.php and manifest.php, and you can commit it, let me know once done, and I will update the website to show the new version.
Is it working in your install or are you not using CAS? Sorry was hoping to demo it to Headmaster on Friday. I have just had a look and I am guessing something big has changed perhaps to do with $guid? Would this mean every line of code that works with dates in the module needs to be rewritten? What do you think?
On the train and mobile hotspot does not let me commit to GitHub. So, emailing you a candidate for v1.0.07, which should fix this issue. Let me know how you get on, and if it works, I will commit and release it.