Cannot filter query MDX

I have created the following MDX Query to determine a date + 91 Days which I am then going to use this as a dataset for a parameter in a SRSS report:  

WITH

	Member [Measures].[StartDateValue] As [Time - Expected Receipt Date].[Date].CURRENTMEMBER.UNIQUENAME
	Member [Measures].[StartWeek] As [Time - Expected Receipt Date].[Fiscal Year And Week].CurrentMember.Name
	MEMBER [Measures].[DayOfWeek] As datepart("w",[Time - Expected Receipt Date].[Date].CURRENTMEMBER.Member_Name)
	Member [Measures].[EndDateValue] As membertostr(StrToMember("[Time - Expected Receipt Date].[Date].&" + Format( CDate(DateAdd('d',91, [Time - Expected Receipt Date].[Date].CurrentMember.Name)), "[yyyy-MM-ddTHH:mm:ss]" ) ))
	
Select
	{
		[Measures].[DayOfWeek],
		[Measures].[StartDateValue],
		[Measures].[StartWeek],
		[Measures].[EndDateValue]
	} On Columns,
		[Time - Expected Receipt Date].[Date].[Date]  On Rows
From
	[Retail] 

Select allOpen in new window

I now want to filter this on the measure [DayOfWeek] to only show the 7's (Sunday) so I do not get duplicates in my Paramter, which I do by amending the code as follows:

WITH

	Member [Measures].[StartDateValue] As [Time - Expected Receipt Date].[Date].CURRENTMEMBER.UNIQUENAME
	Member [Measures].[StartWeek] As [Time - Expected Receipt Date].[Fiscal Year And Week].CurrentMember.Name
	MEMBER [Measures].[DayOfWeek] As datepart("w",[Time - Expected Receipt Date].[Date].CURRENTMEMBER.Member_Name)
	Member [Measures].[EndDateValue] As membertostr(StrToMember("[Time - Expected Receipt Date].[Date].&" + Format( CDate(DateAdd('d',91, [Time - Expected Receipt Date].[Date].CurrentMember.Name)), "[yyyy-MM-ddTHH:mm:ss]" ) ))
	
Select
	{
		[Measures].[DayOfWeek],
		[Measures].[StartDateValue],
		[Measures].[StartWeek],
		[Measures].[EndDateValue]
	} On Columns,
		filter([Time - Expected Receipt Date].[Date].[Date], [Measures].[DayOfWeek] = 7)  On Rows
From
	[Retail]

Select allOpen in new window

However when I run it I get the following Error:

Executing the query ...
Execution of the managed stored procedure datepart failed with the following error: Exception has been thrown by the target of an invocation.Argument 'DateValue' cannot be converted to type 'Date'..

Execution complete


Any advice anyone could give would be greatly appreciated.

Many Thanks

Jon