This site is not for solicitation of services or 'purchasing' development. Please do not post requesting side mods/plugins and so on. Your thread will be removed, and you will receive a warning.
Example: let's say that mod "X" adds a new ore at ID 4000. Pixelmon might have a healer machine at ID 4000. When the game first loads, it looks for these conflicts, and attempts to fix it by shifting the ID's until it finds a pair that is not used.
These ID's for your installation of pixelmon can be find in a configuration file, at .minecraft\config\Pixelmon.cfg (usually inside of %APPDATA%)