Are you using Import Records from the File menu or performing a script?
Open the script and click the import records step. Re-select File from the drop down to the right of the Specify data source check box at the bottom of the script editor.
What do you find in the dialog that pops up?
If the file reference in this dialog looks correct, try using add file to update the file reference to your excel file. I predict that there is some small discrepancy between the two file references or you are attemting to access a file in a shared directory that is not available (maybe not mapped or mounted) at the time you ran the script.
I updated the link, but it was the exact same. However, this morning, all the imports worked without error. I guess if I encounter the error again, I'll let you know. Thanks!