"Err" simply means there is a connection issue with the needle probe and the Blue2/MFT device. We suggest trying the following:

 - Remove the needle probe and thoroughly clean the 2 prong connections. Re-insert the probe and retest. 

 - If cleaning the probe does not work, try another needle probe. The one you have may be damaged.

 - If you do not have a spare needle probe, you may need to purchase a new one.