I encountered the error "Wrong type argument: number-or-marker-p" with theme-changer in a fresh Emacs 24.5 install on Windows 8.1 64-bit. I found no information about this error when searching, but reading through the issue log I found the following:
The solar package seems to get my system time/timezone which was out of sync with the location I specified in my config. Changing my timezone in ubuntu resolved it.
Basically the OS timezone and the Emacs calendar setup need to match. As my home is Detroit but I'm traveling in Europe, mine weren't even close. (By the way, 'solar.el' is included in Emacs by default in recent versions.)