Fatal error: Call to undefined function menu_load_all()
The only thing I can of is that you're calling menu_load_all() in hook_install() or hook_enable(); all system module files aren't necessarily included when those hooks are invoked.

If that's the problem, you can force the file with the function to be included by adding the following line of code to the top of your hook_enable()/hook_install() function:

module_load_include('module', 'menu');