We are using Avaya Workforce Optimization v15 which now uses Microsoft SQL Server Reporting Services (SSRS) as a reporting engine. When one of our customers tried to export a large dataset, they got the error:

Reporting Services Error
Excel Rendering Extension: Number of rows exceeds the maximum possible in a worksheet of this version. Rows requested: 2259767. Maximum rows: 1048575. (rrRenderingError)

On checking on this error, Microsoft documentation states that excel cannot handel more than 1048576 rows on the current versions (reference).

Workaround would be allowing them to export as CSV from SSRS webpage. If CSV option is not enabled by default, you can modify the file

X:\Program Files\Microsoft SQL Server\MSRSXX.XXXXX\Reporting Services\ReportServer\rsreportserver.config

and search for the line

<Extension Name="CSV" Type="Microsoft.ReportingServices.Rendering.DataRenderer.CsvReport,Microsoft.ReportingServices.DataRendering" Visible="false"/>

and set the Visible="true"