3Com 4007 Release Note page 63

Known Problems in Release 3.0.5 63
Each module is allowed a certain number of member ports in a trunk
(L2=6 and L3=8). When you modify a trunk so that the sum of existing
ports plus the added ports is greater than the number of ports
allowed, an error is generated which states that the internal resource
threshold has been exceeded and the ports have not been added to
the trunk.
To workaround this, do not modify a trunk so that the sum of the
existing trunk member ports and the added ports are greater than 6
on Layer 2 modules and 8 on Multilayer modules. Instead, perform a
modification to remove the old ports, and then another modification
to add the new ports. This involves rebooting the module twice.
(30638)