[JasonRiggs]

What I can see in your code is that you are limiting the skins to be either equal to 0 or 300 or 74 or less than 274 or greater than 28 or less than 264 or greater than 267 or equal to 149 or
equal to 311 or 310 or 309 or 308 or 307 or 306 or 302 or 301 or 300, why don't you remove all of that and make it be either greater than 1 or smaller than 312

Code:

if(listitem == 1)
{
new Skin[312], count = -1;
for(new i = 1; i < sizeof(Skin); i++)
{
if(i>=1 && i=<312);
{
count++;
Skin[count] = i;
}
}
if(count != -1) ShowModelSelectionMenuEx(playerid, Skin, count, "Skin Selection", 5, 0.0, 0.0, 0.0);

This is the code which I guess will make it work..