Now my little mining computer is working perfectly but my main mining computer is causing trouble.
After a few minutes of mining (same setting as usual) I get an unhandled exception message for .NET framework:

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.InvalidOperationException: Sequence contains more than one matching element
  at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
  at MultiMiner.Engine.MiningEngine.AddDonationPool(String coinSymbol, Miner minerConfiguration) in d:\Data\Visual Studio Projects\Personal\MultiMiner\MultiMiner.Engine\MiningEngine.cs:line 720
  at MultiMiner.Engine.MiningEngine.SetupConfigurationPools(Miner minerConfiguration, Coin coinConfiguration) in d:\Data\Visual Studio Projects\Personal\MultiMiner\MultiMiner.Engine\MiningEngine.cs:line 701
  at MultiMiner.Engine.MiningEngine.CreateMinerConfiguration(Int32 port, String coinSymbol, DeviceKind includeKinds) in d:\Data\Visual Studio Projects\Personal\MultiMiner\MultiMiner.Engine\MiningEngine.cs:line 626
  at MultiMiner.Engine.MiningEngine.StartMining() in d:\Data\Visual Studio Projects\Personal\MultiMiner\MultiMiner.Engine\MiningEngine.cs:line 553
  at MultiMiner.Engine.MiningEngine.ApplyMiningStrategy(List`1 coinInformation) in d:\Data\Visual Studio Projects\Personal\MultiMiner\MultiMiner.Engine\MiningEngine.cs:line 269