I had the same issue 6 months back...
Though an engineer, my visa was fore-man and my sal is more than 10k.
All the documents were perfect... but when i submitted to the labour dept, without looking into the other documents and salary, they rejected saying "No family visa for fore-man"
The lady there was not even ready to listen to my explaination!
Tried twice this way!
And went on my way to change my visa first and then apply!
It took me 4 months complete the process!! Finally got it!!!

http://www.qatarliving.com/node/1757980