From main menu > Save (screenshot)
We haven’t seen this before. Can you send us the save files to support@greenheartgames.com
should be under
~/Library/Application Support/Game Dev Tycoon/Local Storage
Sent, thx for quick reply… Also maybe because, i start played “old” version (1.3.3) & updated to new one > sshot
given the error message I think the savegame might be too big or something. we will investigate 
Also getting this error on attempting to save games and during posting of the high score screen. Doesn’t seem to impact on the hot save / auto save - I can go bankrupt and restart levels or close the game and reopen without losing data. I just cant create a perm save.
this should be fixed in 1.3.9, which just went live.