H1B visa under administrative processing, issued a pink slip


I attended visa interview today. VO asked me few questions about employer name,client name,client location, project name and salary.
He kept on looking at the system and asked me to submit the entire set of petition. He said he needs to have a closer look at the petition and asked me to wait for sometime. After 30 mins of wait, i was called by the VO and told me that my case is under Administrative processing and issued a pink slip . He didn’t ask for other documents.
I wonder why my case went to Administrative processing?
How long does it take to get my case resolved?

When under administrative processing, you can never tell the time frame. It may take a month or two before they come back with a response. Mostly it will include background checks on you.

What caused it , is purely dependent on what you submitted in the petition.