Updating of OLD queries in Cognos report stuio

[supak]

Hello.
Would you please help me ? I work with Cognos Report Studio , version 10.1.1.
I have query created approx. in 3Q 2015. Now I would like to make some adjustments but because of some reason(s) it's not working.
I try to apply this relatively simple function >> cast ([my_date];varchar (7))  , but it's not working.
When I write this function to new query I created now, it's working without any problem. And even, when I for example replace "varchar(7)" by "date". it's also working in OLD query.

So basically, I can't update my old queries with some functions (which normally works in new query)...."cast" with "varchar" is one example, but there were others as I was told by my colleague.

Do you pls know what can be behind, is there some option in Report Studio that query created in the past is somehow refreshed ?

Thanks a lot.