If the player has no free space to carry the item being rolled.

1. All non-pass buttons will be grey out and disabled.
2. Mouseover any button (include PASS) shows a tooltip to tell the player to clean the bag. OR change the ilvl text or item name text to tell the player about this?
3. When the bag has free space, button will be enabled again.

After this change, ML will rarely fail his loot distribution because some1's bag is full.

Side effect: This could slow down the response process.
So alternatively and more easier, we can choose not to bother with the buttons, and one of the following:

1. Give a big warning when non-pass response is chosen while the bag is full.
2. Big text in the title of the loot frame when the bag is full.

Both suggestions could potentially cause an "unable to award" due to filled bags. With the first, player has 1 free space, and wins two items. With the second he could just ignore it, or maybe even just fail to clear his bags in time.

I don't really want to disable buttons due to full bags - it could take some time to clear out.
Doing some warning text is possible, but then why not just print something to chat?

Either way, I'd very much prefer to relay some information back to the ML. This could be done when awarding (like the current checks, except the candidate sends a "bags_full" comm so we know for certain), or simply just send it whenever our bags are full. I imagine the latter being more reliable, but way more costly. Edit: Probably not if it's only done when we receive a lootTable, and if an award fails, we almost know for sure his bags are full and can use that for the fail message, otherwise we just ignore it.