Message type: E = Error
Message class:  CUMTX - Variant Configuration - Master Data Maintenance 
Message number: 664
Message text: File type for upload must be ".csv"
Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of messages in the SAP system have a message text, however this is frequently insufficient to comprehend or resolve the problem.
To make things easier, more detailed information is frequently added to describe the issue, how to fix it, and the necessary steps or configuration modifications.
Unfortunately, there isn't any extra information in this error notice.
First, use our AnswerBot below to get a possible cause and solution (requires a premium subscription).
Also, review the in-depth Common Questions & Answers listed below; you could discover a solution there or be able to connect with others who have faced similar challenges.
You can also try searching the SAP support portal (support.sap.com) but you need a special user ID to access it. It is possible that an SAP support note exists that provides additional details about the mistake or even steps for fixing it.
The SAP error message CUMTX664 indicates that the file type you are trying to upload is not in the expected format. Specifically, it requires the file to be in CSV (Comma-Separated Values) format. Here’s a breakdown of the cause, solution, and related information for this error:
Cause: Incorrect File Format: The file you are attempting to upload is not a CSV file. It may be in a different format such as .xls, .xlsx, .txt, or any other unsupported format. File Extension Mismatch: The file may have a .csv extension but is not actually formatted as a CSV file. This can happen if the file was saved incorrectly or if it contains incompatible characters or formatting. File Corruption: The file may be corrupted or improperly structured, leading to SAP not recognizing it as a valid CSV file.
Solution: Check File Format: Ensure that the file you are trying to upload is indeed a CSV file. You can
 Get instant SAP help. Sign up for our Free Essentials Plan.
Get instant SAP help. Sign up for our Free Essentials Plan. 
CUMTX663 Document cannot be read
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CUMTX662 Document does not exist or is locked by the user
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CUMTX665 Errors have occurred when uploading
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
CUMTX666 Table is too big for upload
Self-Explanatory Message Since SAP believes that this specific error message is 'self-explanatory,' no more information has been given.The majority of...
Click on this link to search all SAP messages.