problem on connecting devices in eagle
These errors occur when the symbol for a component has its leads marked as 'in" in the symbol view in the Eagle libraries.  Then the other end should be either "out" or "io" (I believe the latter is the default.)  Other choices for pins are nc, oc, pwr, hiz and a couple others.  So you should check pin 25 of the Arduino symbol that it is shown as either "out" or "io" (if you click on the pin in the symbol view, and select Properties, it will show this.)

As far as the RX leads go, it appears you have one RX lead tied to another (RXCAN to RXD).  These would normally both be inputs.

Usually UART leads are cross-connected, so RXCAN would be connected to TXD, and TXCAN would be connected to RXD.  Occasionally RX is an output from a device, and TX is an input, so that RX is connected to RX and TX is connected to TX, but this is very rare. I don't think that's the situation here as I checked the datasheet for the MCP2515 and TXCAN is shown as an output and RXCAN is an input.