This error is returned from a math function when the result of the math function is undefined for the input given. For example the function log(x) is undefined when x is less than 0. If you try and take the log(x) of a negative number you will instead get an EDOM error. Similarly, you can't take the sqrt() of a negative number.

lib/main.php:944: Notice: PageInfo: Cannot find action page

lib/main.php:839: Notice: PageInfo: Unknown action