Did you change MAX_SKILL in mud.h? If so, that's not what you're looking for, MAX_SKILL in mud.h is the total number of skills that you can create, not the level that you can set them at. You should just be able to sset the minlevel of the skill in question to whatever you want it to be. But you also might want to make sure that your immortal levels start higher than the max that a player can achieve in any one discipline, otherwise, that might interfere with the levels you're assigning. Ala:
if( !str_cmp( arg2, "minlevel" ) )
skill->min_level = URANGE( 1, atoi( argument ), MAX_LEVEL );
send_to_char( "Ok.\r\n", ch );
If your MAX_LEVEL is 105, and then your immortal levels start at 101, even if your mortals can reach level 200, it won't let you change the level of the skill over 105.