I think it’s just that the plug-in is no longer there. VirusTotal shows the link to be clean (See: VirusTotal), but it is good to be cautious.
Chris’s final “experimental” beta version of his compressor is available from this forum post: Chris Capel's Dynamic Compressor
The 1.2.6 “release” version is still available via this third party site: Chris's Dynamic Compressor plugin for Audacity