I have been having this issue with Sandstorm since the 1.7.0 update. I am running my own server and when I try to go to certain maps a get a pop up that says serialization error. I have tried the suggestions about removing the mods folder and checking files on both the server and client with no help. I have even reloaded the client and server with no help.
This is not just my server but also my friends server. The weird thing is that two of us can log into one of the servers while the third person gets the error.
I wish someone would look into this rather than just pushing forward with add-ons an updates.
All I ever get is the same old statement to remove the mods folder and check you files.