Did you have to change your VDOP allowable error to a higher number?

FieldLevel will only work with an RTK correction.  RTX will not work.  Additionally, it is recommended that you use a base station that is very close to your project.  Vertical accuracy degrades twice as fast as horizontal and is more difficult to determine.  I was unable to use my Fieldlevel for several years while using RTX.  With my new base station I can use it on fields that are close to home.  I may build a portable base as well.