The first one indicates that the response time of your storage system / datastores is much to high (which can be normal, if some of your VMs sending a lot of IO for example). There can be many reasons for this, eg.: The affected datastore is under contention / huge I/O load, you have some performance problems within your network (regarding you are using iSCSI) etc.
The second message shows that a path to your storage system was totaly unreachable for a moment, which of course can be related to the first error.
Overall there can be many reasons for this problems. I would suggest you to start with checking the iSCSI network.
Regards,
Mario