Errors due to invalid IDs during Data Loader import and update

Salesforce records are either 15 or 18 characters in length.

Typically when viewed within the organization, they are 15 characters: 00300000003T2PG.
When viewed through Data Loader, API, or Apex, they are 18 characters: 00300000003T2PGAA0.

When you use a 15-character, the system may convert the value to the 18-character representation. Invalid IDs will be rejected with one of the above errors. 

Scenarios: CSV file contains an invalid ID in the ID column or the column

1.  ID with invalid characters or ID with length less than 15 characters

• "Insert/Update" operation error: MALFORMED_ID: Object name id: id value of incorrect type
• "Delete" operation error: MALFORMED_ID:bad id 

Error resolutions:

1. Visit the record in the Organization to verify the ID entered. Keep in mind that these IDs are case sensitive. 
2. Manually convert the 15-character ID to an 18-character ID. See article on how to Convert 15-character ID to 18-character ID
3. Verify that the correct field is mapped in Data Loader. If you inadvertently mapped a Text column to a Lookup field, this error might be thrown.

2.  Missing ID (Blank)

• Error: MISSING_ARGUMENT:Id not specified in an update call.

Error Resolution: Enter a valid ID (ID should not be blank)

3.  Incorrect ID (Update/Upsert)

• Error: INVALID_CROSS_REFERENCE_KEY: invalid cross reference id.

Error Resolution: ID should be correct (existing ID) and the Owner ID listed in the CSV file should have access to the record.

See also
Common Data Loader error messages
Insert, Update, or Delete Data Using Data Loader