If you have a semicolon or equal sign as part of your username or password, you receive the login error.
Index was Outside the bounds of the arrays
K2 uses a key/value pairs in the connection string when connecting to K2 servers. Semicolons delineate each property and equal signs separate the key/value pairs, which is why, when you have these characters in your username or password, the server can't parse the connection string properly.
Remove semicolon and equal sign characters from your username or password and try again.