Rainsoft EC4 75v salt tank full of water?

I'd check the salt and see if it has turned to mush in the bottom. Empty it out and start over with fresh "solar salt".

Which is better, block salt or solar salt?

There are a few possibilities.

1.) Where does the system drain when regenerating. A clogged drain line from ice if it drains outside, will cause the system to pump water into the brine tank instead of drawl the brine during the 4th cycle. That's an extremely common problem during the winter.
Is the drain line shoved into a washing machine drain? If it's rammed down there, that can clog it.
2.) I've been servicing rain soft equipment for nearly 10 years. I HATE both pellet and block salt. The mush at the bottom of the brine tank and cause the slits at the bottom of the brine float to clog. It is a possibility that is the issue, but from my experience it's unlikely the cause. Check to make sure the connection to the brine float (white cylinder inside your brine tank) is secure. There is a 3/8" black I.D. tube that runs from that tank to your softener. If they used the provided black line with the equipment. Sometime it's not long enough. So the color is not important. But if there is an air break, the softener will not be able to drawl the brine out of the tank.
3.) Clogged brine injector. Get that replaced or cleaned. Piece comes with lifetime guarantee and shouldn't cost you a penny other than a service charge.
4.) Snapped tab on the brine cam. It will allow refill, but no drawl. Again covered.
5.) Have the flow restricter inside cyclone checked. Sometimes a piece of debris gets inside and will act like a check valve. It will allow refill, but no drawl. Again covered.
Those are the most common problems I've seen. But remember also, that there will always be about 2 inches of water in your tank.