CUDA Mining Error – Illegal Memory Access Encountered

If you are new to mining I would suggest using Claymore Dual Miner. It is very easy and straight forward to run. And you shouldn't have to worry about the errors you're receiving anymore as the program will take care of everything and you wont need to worry about to syncing your node.

I'd suspect this is what has happened.

The current hash rate (as of Ropsten block 673252) is 0.011 GH/s, with the difficulty being 134,588,276.

Prior to the recent spam attacks, if we take block 586946 as an example from before the attack started, the hash rate was ~0.005 GH/s and the difficulty 105,432,944.

The Ropsten testnet was rescued from the spam attack by the donation of significant hash power, which was able to mine a completely new chain starting from before the attack, and replay all the transactions since. I'm suspecting that some of this hash power has remained in the network to help prevent the attack from reoccurring.

You're now mining in a more competitive, but safer, test network.