PIC Microchip TCP IP Lite Stack on 8bit Microcontroller
This issue was raised on the Microchip support forums in January 2019: https://www.microchip.com/forums/m1078511.aspx
From a brief skim through the thread there it looks like the fix for the vlanId error on line 58 is to simply comment out the entire union, since it's not used.
It also appears that you need to configure the compiler to use the 'C90' standard instead of the apparently default 'C99' setting, and this will probably resolve the errors with the other bit-fields.
Also:
https://www.microchip.com/forums/m1112846.aspx
https://www.microchip.com/forums/m1064359.aspx
seem to mention similar 'solutions'.