We will, if we can
send some crash report or log data, otherwise i cant say where the problem exactly is.
If you need help and tipps with installing mods we could still try to find a way.
Sadly it is not so easy to set up a server and it takes a lot of time, if you want to install many mods by your own.
But if you send us some log data or crash report we could try to figur out where the problem is and try to solve it.
if i get it right then you say that:
if u put mod A on the serer it works fine. if you put mod B on the server then nothing works.
and if you try B first and then A, the same issue happens?
what mods are we exactly talking about?
the error message means that the server cant start at all and crash, so there should be a crash report would be nice.
First of all, some more informations would be nice:
what type of server do you use? (bukkit/spigot, forge...)
if you get a crash log, please post that too.
and what types of mods do you want to install?
i would guess that you try to install a mod that would not run with the installed version of the server or maybe it interruppts with an already installed mod.
sometimes you have to use an older version of the mod, to make it run on the current server version.