Firm and partners are jointly and severally liable for payment of sales tax dues

2)  

Notwithstanding any contract to the contrary, where any firm is liable to pay any tax (including any penalty) under this Act, the firm and each of the partners of the firm shall be jointly and severally liable for such payment:

Provided that where any such partner retires from the firm, he shall intimate the date of his retirement to the Commissioner by a notice in that behalf in writing and he shall be liable to pay tax (including any penalty) remaining unpaid at the time of his retirement and any tax (including any penalty) due up to the date of his retirement though unassessed on that date:

Provided further that if no such intimation is given within fifteen days from the date of retirement, the liability of the partner under the first proviso shall continue until the date on which such intimation is received by the Commissioner.

3) you have not mentioned period for which claims have been made 

4) Partnership deed and deed of retirement must have been registered with registrar of firms 

5) take search in registrar of firm for copy of partnership deed and deed of retirement 

If you have received a notice from the taxation department then it becomes your duty either to pay the tax demanded or to defend your interest by producing documentary evidences to prove that you are not liable to pay any such taxes. 

Whether you were a dummy partner or an effective partner, as far as the partnership registration deed is concerned you are a partner of the firm 

You canot say that you ere just an employee hence the salary you received is the salary allotted to the working partner, therefore on that basis you cannot claim yourself as an employee. 

You may consult a local advocate , discuss the subject matter at length and proceed as suggested. 

You are victim of fraud by your employer. Reply to the notice  stating the facts and file a fraud case against employer. Only if you file fraud case against him you can prove your innocence.