Strict Standards messages
The strict standards messages are appearing, if in the System → Global Configuration → Server → Error Reporting is higher, than Simple. The System Default should be fine too, because in most cases that is on Simple. This isn’t an error message, only a warning, which you can ignore, so just change the Error Reporting to lower, and it will be fine. After this you might need to go to the Smart Slider’s Settings → Cache, and click on Refresh Slider.
If you don’t want to turn the error reporting lower, then delete this folder with everything in it, and that will solve it too: