ok, i just had this problem. and i hate to sound redundant but it’s worth saying if it saves anybody any stress. check the hostname information!
i too copy and pasted the info they gave me at 1&1 and it didn’t work. HOWEVER, i noticed when i look at info in the MySQL Administration of the control panel on 1&1, it’s slightly different than the info i originally copied. not sure why, but for some reason there were extra letters at the end of the original info they gave me.