Making a block diagram and I get the error "missing source signal"

For these errors, it looks like you've got a "rogue" wire that is messing up the connections as well as missing signal wire names. Draw a selection box around pins where you have the little dots and x's and delete the extra little wires and fix the connection.

For the signal naming issues, for example, you have a 2 bit bus (B[1..0]) and then a single bit wire going into inst13. If only one bit of the B bus is to go into inst13, you need to add a signal label to that wire (named B[1]) for example. This type of fix is required in a number of locations.