Check to see whether the machine running LinkFixer Advanced is set to enforce FIPS encryption standards.
FIPS refers to the United States Federal Information Processing Standard (FIPS) 140 standard that defines cryptographic algorithms approved for use by US Federal government computer systems for the protection of sensitive data.
Here is a link that explains why you are having trouble: https://blogs.technet.microsoft.com/secguide/2014/04/07/why-were-not-recommending-fips-mode-anymore/. The most telling section is "Why FIPS mode is particularly onerous".
LinkFixer Advanced is a .NET application that uses some basic cryptographic functions to create hashes of child files, when those child files are not supported file types. These basic functions are not FIPS compliant. As a result, LinkFixer Advanced will work on your server machine only if you disable FIPS (at least temporarily).
If you cannot disable FIPS on this server, another solution would be to simply move LinkFixer Advanced to a workstation, virtual machine, or even a laptop that is not set to enforce FIPS. As long as that machine is on the same (fast) sub-net as the server, you should still get good performance.