Most browsers allow setting security levels, and if set too high cookies may be rejected and/or some sites may be blocked. In that case you can usually set a permission to allow a specific site, or allow cookies from a specific site, simply by putting the site name in a list somewhere.

I haven't heard of an AV having a problem with mudcat, but there should be a way to specify an "ignore criteria" for a specific site that you trust. The protection against "unsafe internet access" sounds more like a "content filter" function such as one would use to prevent the kids from getting to unsuitable places, and you may have something set in your browser and/or in your AV, so it could be either program that's causing the problem.(????)

John