For some reason if you are transferring agents from one base to another and either the sending or receiving base has a full alien containment, the transfer is refused even if living space is available
Agents DONT use Alien Containment to live in ;)
The issue also appears to apply to store items and equipment transfers as well!
Problem persists as of 11th/10/2018
Alien containment not even full!

From a quick look at the code....
When any transfer is done it checks everything even if it's not affected by the transfer.
transferscreen.cpp, line 293
`
if (vecChanged[i] || forceLimits)
{
crewOverLimit = b.second->getUsage(*state, FacilityType::Capacity::Quarters,
vecCrewDelta[i]) > 100;
cargoOverLimit = b.second->getUsage(*state, FacilityType::Capacity::Stores,
vecCargoDelta[i]) > 100;
alienOverLimit = b.second->getUsage(*state, FacilityType::Capacity::Aliens,
vecBioDelta[i]) > 100;
if (crewOverLimit || cargoOverLimit || alienOverLimit)
{
bad_base = b.second->building->base;
break;
}
}
`
it could set flags for whether there's been any transfer of a particular type. Alternatively any measure that prevents over-filling of alien containment should solve it.
Logically, we only want to do checks for what is transferred with regards to space/money/effect on organisations/etc.
This should be updated every-time an item or item type is modified by the user
Not sure if that's easy to work your magic on though?
See also #505