Importing Tasks From Excel
Please read the section Things to consider section before importing any tasks.
To begin, select the "Task Manager" option on the navigation bar

From the Editor Ribbon Page,

From the "Import" group, click the "Excel Import" button
Select the file to import from the File Open Dialogue Box

Click the file open button and the import process will begin.
When the import has completed, one of the following message will be displayed

The above message will displayed when the import is successfully.

The above message will be displayed when the import has failed was aborted.
The most likely cause for this message, is that the file was either not exported from MS Projects, or did not contain the correct workbook name.
Repeat the export process and make sure you select the "Task and Resource Pivot Table" option from the export map list.