The . prefix won't do anything if the dll is using SendMessage to communicate with mIRC, which is probable given that this stuff is likely being run from the LoadDll() function (the only way to explain the first-run-only behaviour).
The OP already admitted the dll he has is a "pre-release" version. I'm sure it's built with some debug flag set. An easy way to solve this problem is to just stick to normal dll releases rather than take the long route of debugging the entire script.
