capital gain problem

NO, unless immovable property.

Conversion of Capital asset into stock in trade is treated as transfer, capital gain will arise in year of transfer but taxable in year when the stock is sold.
Exemption u/s 54EC is available if capital asset is immovable property and the period of 6months(for investment) shall be calculated from the date of sale of stock in trade and not from date of transfer of Capital asset to stock in trade.