ssas mdx and t-sql gives different values

My situation:

There is a work database. Every day it is copied to another database named RetailDB. Fact and dimension tables of SSAS are based on VIEW-objects of tables in RetailDB.

So, I have the problem:

MDX query:

SELECT{[Date].[Y-M-D].[Day].[01.01.2013]}ON0,{[Measures].[Quantity]}ON1FROM[Company]

gives me NULL value

at the same time t-sql query:

SELECT SUM([Quantity])FROM[RetailDB].[dbo].[fact_Income]WHERE Day ='2013-01-01'

gives me 7937338,023

On other date MDX-query can return correct value.

On some other date MDX-query can return not NULL value but it does not equal to t-sql value.

Please, help to correct this problem. What should I check in my cube to fix this?

Thanks for everyones answer.