When you get a bunch of “frame too long” errors, it typically means that the device connected to the other side of the connection is sending frames that are over 1500 bytes long. This can be because one of two reasons:
1) The other device is configured to send VLAN tagging information (1518 bytes long, or sometimes 1522 bytes long) and the local interface is not configured to respect VLAN tags and only wants to see 1500 byte long frames
2) The remote device is configured for jumbo frames (9500 bytes long) and this interface is not configured to handle jumbo frames and wants to see only 1500 or 1518 or 1522 byte long frames.