Past Continuous vs Pr.Perfect Continuous

I got lost in the English grammar. Could you please answer me one question. There are two sentences:
1. I was eating an ice-cream, when he entered the room.
and 2. I have been eating an ice-cream, when he entered the room.
What's the difference between them?
As I know in oral speach noone will form complicated grammar constructions, speaking about Pr.Perfect Progressive, for instance. But what about classical English grammar?
Thank you in advance!
Aida

The second is wrong- the present perfect continuous has a relationship to now. People will use the present perfect continuous in speech. We often use the past instead of the past perfect, and tned to use simpler language when speaking colloquially, but the present perfect continuous wouldn't be on that list.