Common Errors:
1) Invalid date format:
Sometimes when you upload the offline event .csv file, the date format might be incorrect, and this will throw an error.
The only recommended date formats are as below, please refrain from using any other format.
yyyy-MM-dd
yyyy-MM-dd HH:mm:ssZ
yyyy-MM-dd HH:mm:ss.SSS z
yyyy-MM-dd HH:mm:ss.SSS
2) Invalid Unique Id :
When you enter an incorrect email address format in the import file, the system will throw an error, or sometimes when the email address is not present in the system then it would throw the same error. Please make sure that the contact email address is present already in the system
The excel sheet had two email addresses out of which one had an incorrect format, hence no. of events uploaded was 1 instead of 2.
3) Invalid Email
Sometimes we might import an invalid email address and below is the error that you will receive, please check the contact’s email address, and import the file again to fix this issue. 
4) Others:
This is a rare error that we could see in the offline event import, any minor mistakes made in the field label or special characters present will be captured under “others” error status.