[gmatelich]

I assume you are using WorkManager or ModelManager, if so, you will need to reserve or set modify the model through the WorkManager or ModelManager interface.
Reserve unlocks the model and reserves in it WM or MM so others know you are working on it.
Set Modify unlocks the model only in Modeling so you can work on it, but when you save your work you will only be offered the option of revising the model, since it is not reserved in WM or MM