I'm getting this error: Unknown error (0x80005000)

First of all, let me tell you that my code works fine during the day, but each morning when the user tries to connect, the following error is thrown:

System.Runtime.InteropServices.COMException: Unknown error (0x80005000)

Yes I'm using LDAP, what is funny is that everything works fine until next day. Restarting the application in iis solves the problem, but I have to do this every day so how can I fix this issue? I'm thinking that maybe this issue is in the iis, does anyone have any idea?