When doing an import in the SQL*Loader Wizard - if there is an @ symbol in the path / folder name, Toad replaces the @ symbol with 'XE', or '11G' (or whichever version of Oracle is in use).
This also prevents a successful export with the Export Wizard, if there is an @ symbol in a folder name.
Where the @ symbol is shown initially in the path, when it comes to import, or export, this is changed and the import fails.
If you don't have an @ symbol in the folder name, it works fine
This is an issue with SQL*Loader, rather than a defect with Toad.
WORKAROUND:
Remove the @ symbol from the folder name.
If you get Toad to just build the parameter file, if the parameter file already has the substitution, then Toad is at fault.
If the parameter file is correct, please run it from command line SQL Loader and see if the issue happens. If so, it is an issue with SQL Loader.