Problems for Japanese users with ELS

We have some (but not all) Japanese users reporting errors at the point in our startup where we read the ELS (Encrypted Local Store).

We've run a test application that saves and reads objects to and from the ELS. When reading an object we just wrote, we get an error ("general internal error"). When we read an array of these objects, we get a 2030.

The test class has only simple data types and does not implement IExternizable. It has a [RemoveClass] tag.

Any ideas?