When doing the challenge for the Automate Basic Business Processes with Process Builder, I keep getting the following error:
Challenge Not yet complete... here's what's wrong:There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Account number must be 8 characters long.: []

I moved on to the next challenge in Collect Information from Users and then Operate on It with Visual Workflow and I am receiving the following error message: 
Error element Create_Account (FlowRecordCreate).
This error occurred when the flow tried to create records: FIELD_CUSTOM_VALIDATION_EXCEPTION: Account number must be 8 characters long.. For details, see API Exceptions.

I am thinking there is something wrong with the account number, but I don't know how to fix it.  Can anyone help?