Why is Microsoft Communicator saying someone is offline when they are online?

[Asgar]

It looks to me that every few minutes my colleagues appear offline if I know they are online right at their desk, then it gives me an error message that states "The following message could not be delivered to all recipients,
possibly because one or more persons are offline". Even tried some friends near to me, but it clearly says they are online on their status screen but it says offline on my screen. By the way I am running Microsoft Office Communicator 2005, can anyone please help me out? Thanks.

[Anywhere]

We used to get that same things when users were connected over wifi. When the user gets dropped and reconnected frequently, then it will take them offline and then bring them back again. I dont know if this is the case with you, but you can try it out for yourself. There is also another possibility that they might have blocked you.

[techman]

Even I have experienced that many times, I have noticed that when the user decides they dont want to be bugged and so they set their status to "Appear Offline".

[Asgar]

It is really sad that there is no way to customize that for any person that I want to.