After running loadbuilder I get a message that says "The layer <Layer_Name> could not be opened."
This seems to happen when Loadbuilder cannot open a geodatabase feature class.
These are some ideas to try to resolve the issue.
You will need ArcMap installed in order to be able to do this.
Add the feature class to the table of contents
Right click on the feature class and choose Data > Export Data
Troubleshooting and Understanding LoadBuilder