Here is a common problem. The index points to a PDF but the PDF name is not the same. One way to fix this is to look inside the index (.csv file) and rename the PDF file to match what is in the index.
Another way is to use the Link to new PDF command. Be aware that this will remap ALL entries in the index to the chosen PDF. So you cannot use this for indexes that point to multiple PDF files. This will basically remap all entires in the index to point to a single PDF.
Here’s how to do this:
1: Open an index and press Edit Index
2: Press the downward v (in this picture to the right of Colorado)
3: Choose Link to new PDF and choose a PDF file to remap all entries in the index to.
Once you choose a new PDF, all of the index entries will point to the new PDF.