Hello,
this error is only possible if you have multiple copies of Hibernate Search attempting to write on the same path, or if the path you are pointing at is a network share as such filesystems have occasionally proven themselves unreliable regarding to file locking.

So could you check if:

• the two applictions are indeed writing on different directories
• are you sure you don't have multiple applications using Hibernate Search in each JBoss, who might also be writing on some shared directory?
• is this /Folder_Path/ on a network share?