I got this error today too a couple of times. Here's what I have in the log:
System.Exception: Failed to save game 'autosave'. Exception: System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
at Microsoft.Xna.Framework.Media.ImageStream..ctor(Color[] colors, Int32 sourceWidth, Int32 sourceHeight, XnaImageFormat format, Int32 targetWidth, Int32 targetHeight)
at Microsoft.Xna.Framework.Graphics.Texture2D.SaveAsImage(Stream stream, XnaImageFormat __unnamed001, Int32 width, Int32 height)
at ad3.a(Texture2D A_0, String A_1)
at bef.b(String A_0)
at bef.ac5(String A_0, Boolean A_1, Boolean A_2) ---> System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
at Microsoft.Xna.Framework.Media.ImageStream..ctor(Color[] colors, Int32 sourceWidth, Int32 sourceHeight, XnaImageFormat format, Int32 targetWidth, Int32 targetHeight)
at Microsoft.Xna.Framework.Graphics.Texture2D.SaveAsImage(Stream stream, XnaImageFormat __unnamed001, Int32 width, Int32 height)
at ad3.a(Texture2D A_0, String A_1)
at bef.b(String A_0)
at bef.ac5(String A_0, Boolean A_1, Boolean A_2)
--- End of inner exception stack trace ---
at cez.LogAndThrow[T](Exception innerException, LogSeverity severity, String message, Object[] messageArgs)
at bef.ac5(String A_0, Boolean A_1, Boolean A_2)
at nf.cz(aj8 A_0)
at zq.g(aj8 A_0)
at ba6.cz(aj8 A_0)
at zq.g(aj8 A_0)
And it once failed to load the autosave it did when failing to transition. It stopped happening after exiting and opening the game again, though and was able to access any area I tried.
This is on W7 64bit, i7 2600k, 24GB RAM, GTX 460
Oh, and version is 1.0.0.0 mostly because I'm afraid if I update during a playthrough something will go wrong.