There are two things I would check if I was experiencing this issue:
1) I would make sure the Slingbox is streaming in TCP. To check this while at a remote location, you can, while you have the stream running on your iPad, tap three fingers on the iPad screen to bring up the Diagnostic screen, and see whether it says TCP or RELAY under Connection. If it is not TCP, I would suggest setting up port forwarding on your router for port 5301.
Here is an article that can help:
2) I would also make sure the Chromecast is using the adapter plugged into a wall outlet or surge protector, rather than using the USB cable into the TV for power. While using the USB into the TV for power may be enough to run the Chromecast device itself, it can cause problems when trying to stream to the Chromecast from Slingplayer.
Hope this helps!