The exact reason for the rejection can only be obtained if your (potential) employer contacts the immigration department but here are few possibilities:

1) Your potential employer did not (or could not) obtain labor approval for 1 additional visa (for Indian in this case);

or,

2) You might have a blacklist record either in Qatar or GCC;

or

3) A person having similar name to you has a blacklist record either in Qatar or GCC.

Hope it helps!