(See the best response by Higoten.)
Hello, I am a new user of BYOND and mostly I play space station 13, recently a strange problem occurred for me that disables the ability to play anything on byond, when I open any window in the game client, like I use a computer in the game I mostly see <.B> <./B>stuff stuff stuff... in one row, and byond is trying to open (I think it is byond) using Internet Explorer or Adobe reader (I have deleted AR to check if the file will be still opening) a randomly file(s) from directory /Documents/Byond/cache/ and its opening it multiple times not only once.

-I made multiple uninstalations of BYOND and instaling it again, blocking the file(s) with a firewall.
-Deleting Catche normaly, and deleting using properties option.
-Runing from diffrent users by the number of 2 + guest
-Changing User directory, as well instaling BYOND in diffrent partictions and directiries.
-Changing a bit in properties

also sharing the print screen of the thing:

Best response
Try upgrading to the latest version of Internet Explorer, or, if your using a windows version lower than Vista, then uninstall and reinstall Internet Explorer.

Check your firewall settings as well, the "Navigation to designated website was canceled" error message seems like something is blocking it, being its trying to access a local file.

If none of that works, It might be some crazy security feature that Microsoft has embedded in Internet Explorer. Here is a link that has some steps you can follow that may help in resolving this issue. The steps you can take to fix it are about halfway down that page.
I updated Acrobat Reader and IE, didnt worked, but when I uninstaled AR EVERYTHING started to work fine !
thank you Higoten!