I am getting this error as well. These are WAV files from record recordings. But I also get it for other files I am trying to clean, such as FLAC and mp3. It occurs when I am using the de-rumble features on the dashboard for "Denoiser." I also get other errors under that -- "Error while writing noise sampler file" comes up when I try "Cassette recorder remove noise" and when I try to remove 60hz hum I also get the "Error while..." message.
I think it's an error on the install of version 4 -- never happened before. But there was a bit of a "hiccup" when it installed and perhaps it was installing that section of code. I checked -- there are no updates to the software yet. But yes, I will contact them in a day or so. Perhaps someone will post more information in the meantime.
@Greybelt You can try a free tool like Revo Uninstaller to completely remove ACL4 from your computer including all its registry entries. Then try to reinstall it with your firewall or Windows Defender temporarily disabled, so no files will get accidentally deleted by them. Maybe it will help.
I received an answer from tech support. They have replicated the problem and wrote that they have... "...formally escalated the matter to development. I'm standing by for feedback to find out what implications those error messages even have, whether a technical explanation (and thus maybe manual support solution) is available, and what kind of priority this problem will have in development for a solution on the end of the software. If I get feedback shortly, I'll keep you posted on this situation."