I see three alternatives:

• or blockList is null
• or blocklist contains null values...
• or blocklist contains values that are not of type block

I'd test with this code:

foreach (Block block in blockList) { if (block == null) { System.Diagnostics.Debugger.Break(); } block.Draw(spriteBatch); }

I see three alternatives:

• or blockList is null
• or blocklist contains null values...
• or blocklist contains values that are not of type block

I'd test with this code:

foreach (Block block in blockList)
{
  if (block == null)
  { 
      System.Diagnostics.Debugger.Break();
  }
  block.Draw(spriteBatch);
}