Message: Failed to create data load adapter "%s"
This can happen when the data load system is trying to load an adapter that doesn't exist or is unavailable on the filesystem or if the file exists however the appropriate class name does not.
Data loader adapters are stored in the "/libraries/joomla/database/loader" folder, so if the file is not located there either an invalid adapter has been requested (via JDataLoad::getInstance) or the file exists however an invalid class name has been specified.
If the file doesn't exist, review the code that triggered the issue in question and validate that it is requesting an appropriate adapter. If it is requesting the appropriate adapter then ensure that the adapter has been installed onto the target site.
If the file does exist, open the file up and validate that it is using the correct naming convention. Data load adapters use the prefix "JDataLoader" followed by the name of the file.