If Essbase cannot open the Essbase - Data Source that you want to Essbase - (Load|Build) Cube Processes, ensure that the following conditions are true:
Essbase can load only data sources that are not locked by another user or application.
Text files must have a .txt extension; rules files must have an .rul extension.
Check for misspellings.
Ensure that no one has moved or deleted the data source.