I'm so sorry to hear this is happening. Receiving this error message when importing a .csv or .xlsx file is something we are continuing to troubleshoot. Was this file downloaded from an outside system? A workaround we suggest in the meantime is saving the .xlsx file as a .csv. You can then upload this list as a .csv or even switch the file back to an .xslx after making it acceptable.
Frankie P. Community & Social Media Support
Did I answer your question? If so, please mark my post as an "Accepted Solution" by clicking the Accept as Solution button in the bottom right hand corner of this post.