What error message does the Time Series Forecasting platform say? Is it something like in this screenshot? If so, that means your series probably has duplicated timestamps, e.g. 07/2015 appears twice or more in Customer Y's series. Even a series or more has problem, the platform should be able to analyze other series that don't have problems.
Data quality is a challenge during forecasting many series. Group Summary of Time and Group Summary of data can help to reveal difficult-to-spot issues.