What is, Example, "File B18:4/4 Len:1"

I did a Cross Reference Report the only occurrence of a bit "B18:4/4" and with it on the next line down I see this;
"File B18:4/4 - MSG - File #2 (Name of Project) -3 Len:1
My help does not work.
This bit I believe is some kind of handshake file. It keeps coming true when it's not suppose to.

Looks like message instruction reading from another PLC overwriting word B18:4.

Post your program if you can. Zip it first.