I had a similar problem that I could not get the box checked in line 92 of the California form 540 when I specified that someone could claim me as a dependent. It seems that the issue that if you specify that someone else can claim you as a dependent, then later on TurboTax skips the part where it asks you about your medical coverage.
Here is the workaround I found: first go back to the "My Info" and change your selection to say that no one can claim you (this is only temporary), then go back and edit your state return and TurboTax will now let you specify if you had medical coverage. When you're done updating the medical coverage info, you go back to "My Info" and change it back to say that someone can claim you. This worked for me to get the boxes checked on both line 6 and line 92 of my 540.
