if most of your 770 inputs are very small the problem could be that the fee for including it in a transaction is bigger than the input itself.
a transaction with 770 inputs will be bigger than 100KB (non standard as in ck's response), so do not try to send everything at once.
in Armory I would try to set a really low fee (1 or 2 satoshis per byte) as with the standard value of eg. 200 sat/b the fee for a single input can be as high as 0.0004 BTC, so including any input below that value would be pointless. Armory might be smart enough not letting you spend them.
Only try to send a transaction with such a low fee when the transaction memory pool of the network is nearly empty - I successfully had transactions with only 1 sat/b executed waiting for less than 6 blocks.
consult
https://bitcoinfees.21.co/#delay to check how long you expect to wait depending on the fee included. At the time of this writing a tx with a fee of 1 sat/byte should be included within the next 3 blocks
