Importing a PST file is a lot different then importing data from a CSV (comma separated values), Microsoft Excel or Access file. If attention isn’t paid to the actual steps required, it can result in the <appearance> that the import was not successful. Whether the PST2PST import process should be used at all is also a question that needs to be addressed.
This video goes through the most important elements when importing data from another PST file.
PST2PST Importing – How it differs