I don't think you can use the myval.Highbyte etc. in the I2C instruction.

From the manual:

"If a word-sized Var is specified, 2 bytes are read and stored into the Var high byte first, followed by the low byte. This order is different than the way variables are normally stored, low byte first."

Looks like you just use the variable (WORD) as is. Pay attention to the loading order.