@emrgohff: For me that looks like that you've many inputs (from mining, staking, PoB minting etc.) in your wallet. Maybe to get an idea you could post the (approximate) number of incoming transactions you received, or how long you are PoB/PoS minting or mining already? (if this is too private you can send me a PM)

If this is the root of the problem, then you should try to consolidate the UTXOs. This means convert many transaction outputs into a few transactions sending them to yourself, which will make your wallet "cleaner" and your Slimcoin client will work faster. The easiest way should be to make a big transaction (as big as possible without the above error) to one of your own wallet addresses first and then use Coin Control to consolidate the rest. Can be a bit tedious but is unfortunately currently not possible automatically. If you need more instructions (don't know about your knowledge level regarding Bitcoin-based coins) simply post your questions.