The reason you got an error message when a 6 port fibre card in the first slot is because this is for a clocking/ Frame sinc card which you obviousley need when using dig services (BRI/PRI) the Modular ICS has a max capacity which is calculated when using a 6 pt fibre, a 2pt & 6pt can't co-exist also the DTI card would go in slot 4. to keep your existing programming/ provissioning of channels. you would need to upgrade through the s/ware levels eg: your on 4.x & want 6.x save data, switch of sys remove s/ware cart insert 5.x power back on (check setup- it should be the same) power switch off then insert 6.x, power back on & you should have retained all of you current setup (works for me)