I tried to send the contents of my wallet, around 600 mBTC, consisting of around 2900 bitdust transactions, and received the message:
Error: Transaction creation failed!
I understand the reason.
If the transaction has so many inputs that it is larger than 100 kilobytes, you can't send it. Since a typical input is larger than 40 bytes, you'll run into the maximum transaction size before you run out of funds for the fee.