I'm no expert on this, but from the little research I have done on this, I was told that you have to buy a license for the Search Module.

You need to purchase a license for DX Search Module. ISE is licensed by the number of DiskXtender servers that are submitting files to the ISE. (Each server can manage one or more extended drives, each of which can submit files for indexing.) You can license as many as 10 DiskXtender servers for a single ISE server.

The ISE is installed automatically with a 30-day evaluation license. When the
evaluation license expires, indexing is disabled. However, you can still search for filesthat have already been indexed.