Sim4Life light can only open projects created with Sim4Life light, which should be the case for the tutorials that get installed when you run the installer. You probably tried to open some tutorial projects created by the full version. It is of course possible that it is a bug, but please double-check that you are opening the tutorials installed as part of Sim4Life light. The easiest way to be sure of that is to click "File -> Open Tutorial" from within Sim4Life light, as it should put you at the right location.
Note, however, that if you (or someone else) opened these tutorials with the full version of Sim4Life and saved them (intentionnally or not..), then it will not be possible to open them again in Sim4Life light.
If you are not sure, simply get the latest version of Sim4Life light online, uninstall the one you have (which shoud remove the existing tutorials, but you can double-check), and install it again.
I hope this helps