black listed visa /passport

hi there,
if anyone could help me out with these term "black listed visa /passport". how does it get its term and is there any way to get out of the blacklist?
i have a friend of mine with this issue. the company said he is in blacklist....but somehow he managed to get back in Doha.
looking forward for some clues
Thank you.
how check if a person can go to doha if he banned from the country
Hi, i was working for company on business visa and now i have taken exit saying on emergency leave. Luckly i have got offer from other comapny and they have sent work visa as well. now can i re enter the country with work visa of second company and my worry is wheather my first company knows that already i got visa from other company and they black list me... so how will i know am free to take entry once again on work visa...
first, "blacklisting" has its validity, i.e. it's expires in certain period of time. Second, if the reason for blacklisting was not too serious, there is the way to get "un-blacklisted"...
*********************
“You become responsible forever for what you have tamed”. Antoine de Saint-Exupéry