There aren't many FAQs yet, but here are two that seem to come up occasionally:
I get "Fatal Error: Call to undefined function createimagefromjpeg()" when I try to upload an image
Your version of PHP probably does not have GD enabled, or it was compiled without the jpeg library present. If you want to use the image abilities of TankLogger, these things need to be enabled. For more information, visit:
PHP Image Functions
JPEG library
I get "Fatal Error: Call to undefined function xml_parser_create()" when I try to update the head loss calculator
Your version of PHP was probably either built with no Expat library present, or it had XML support turned off with --disable-xml when configured. Please see XML within PHP for more information.