When registering a custom SSRS report, selecting the correct report-specific DSP (Data Source Provider) class is critical. In your case, this should be the DocSalesQuotationDSP class.
(Note that selecting the Default DSP class may cause some of the features available in the Full Edition to not work correctly. For more details, please refer to the how-to manual)
Also, the DSP class you selected (3) should match the DDSP you used to design your custom template (4). In case there is a difference between these, the validation will not succeed.
After you have initiated the validation, please inform us about the result