Looks like a comunication error. It could be a physical problem, with the wiring or termination, a configuration problem with in the drive, or wrong settings in Linuxcnc. (really just about any thing.)
First thing to do is research you drive's manual to see how to configure it for modbus control (most drives require you to set several parameters to enable it), and find out what it's port settings are/should be (baud rate, slave id, parity bits, stop bits, data bits, register addresses...). Then you need to make sure that you've setup Mb2hal to use those exact same settings.
I found it was easier to test modbus communication with my drives using Classicladder and make sure they worked, before I set up Mb2hal. (In fact I probably would have preferred to just use CL if It could have handled twice as many transactions as it does.)