Getting an error message starting Model file ended prematurely... indicates that the model you are trying to open didn't save correctly. In most cases this is caused by a bug that happened in ExtendSim releases earlier than 10.0.5 that if you accessed the properties of a hierarchical block (either by right-clicking or by using the command Ctrl+i) before you saved the model.

Unfortunately, you probably won't even realize there is a problem until you try to open the saved model. The error message could look like either of these two screenshots, and mention DRAWOBJECT tag or notebooks tag.

If you encounter this error message when trying to open a model file, it indicates the file didn’t save properly after you created a new hierarchical block.

• Do not try to access the properties of a hierarchical block in your models unless you have a more recent release of ExtendSim than 10.0.5.
• Update to ExtendSim 10.0.9 as it contains a fix for this issue
• Open the ExtendSim backup model (labeled *.mox.bak) in 10.0.9 as the original model was probably corrupted.