Here's what I did to stop the message from being shown.
In mob.h around line 38 I added:
	Code:
	#define APPEAR_LEV	   0x0013
 Then in client_process.cpp find these lines:
	Code:
	else if (sa->type == APPEAR_HEIGHT)
{
   entity_list.QueueClients(this, app, false);
}
else {
   cout << "Unknown SpawnAppearance type: 0x" << hex << setw(4) << setfill('0') << sa->type << dec << " value: 0x" << hex << setw(8) << setfill('0') << sa->parameter << dec << endl;
}
 In between the else if{} and the else{} I put this in:
	Code:
	else if (sa->type == APPEAR_LEV)
{
   entity_list.QueueClients(this,app,false);
}
 So it should look like this:
	Code:
	else if (sa->type == APPEAR_HEIGHT)
{
   entity_list.QueueClients(this, app, false);
}
else if (sa->type == APPEAR_LEV)
{
   entity_list.QueueClients(this,app,false);
}
else {
   cout << "Unknown SpawnAppearance type: 0x" << hex << setw(4) << setfill('0') << sa->type << dec << " value: 0x" << hex << setw(8) << setfill('0') << sa->parameter << dec << endl;
}
 This seemed to work fine for me.