Daedalus wallet can get into a state where the value in the wallet is spread out over so many addresses that when you try to create a transaction the transaction size exceeds the maximum size (in terms of data, not Ada). This causes an Amount too big due to wallet fragmentation error as of Cardano Version 1.5 Daedalus Version 0.13.0
Transaction size in terms of data is limited to ??, partly because some of users were posting pictures to the blockchain, but also for other technical reasons.
Create a transaction that will consolidate small amounts of Ada spread out over many addresses into one address by sending Ada to yourself. The amount of that transaction has to be less than the limit so as to avoid the Amount too big due to wallet fragmentation message