Invalid data type error when parsing class fxptui.explorer.

I'm attempting to run a simulation using MATLAB and Simulink. However, I'm receiving this error:

"Warning: an error occurred while parsing class fxptui.explorer:
Invalid data type.

> In fxptui.getexplorer at 9
In fptoolcallback at 34"

Can anyone tell me what this error is and how to fix it?

[Danny S]

I'm also seeing this on a save_system() call to a Simulink Library I just created and populated with new_system()/add_block().

It's showing on Linux (Ubuntu 10.04) with Matlab R2011b 32-bit. The same sequence of calls on Windows 7 / Matlab R2010bSP1 does not produce this warning.

[xlr8t]

I'm also seeing this with a call of

sim('simulink_model')

with slightly different line numbers.

[Warning: an error occurred while parsing class fxptui.explorer: Invalid data type.]
[> In fxptui.getexplorer at 9
   In fptoolcallback at 7
   In myFunction at 185]

where the line 185 is the sim command. The system used is a Linux with Matlab 2012b (R2012b (8.0.0.783) 64-bit (glnxa64)).