It's hard to say why this is happening without more data. When does it happen? During doc open, save, or publish?
Do you have any customizations, such as scripts running during the process that shows the problem?
I would start with the warning for your time-independent variable, as that may have something to do with it as well. This would lead me to believe you need to look into your stylesheet modifications. Did these errors start happening after specific changes were made?