Folder monitoring

A weird happening....
For no apparent reason I seem unable to monitor a rule by viewing the file it refers to. First time its happened and don't think I I've made any major changes that would affect the operation - any thoughts?
I have attached the onscreen warning below...
[img][https://imgur.com/a/cD7uT9[jimg]
For no apparent reason I seem unable to monitor a rule by viewing the file it refers to. First time its happened and don't think I I've made any major changes that would affect the operation - any thoughts?
I have attached the onscreen warning below...
[img][https://imgur.com/a/cD7uT9[jimg]