Attempt to create a transformation results in error "transf. does not exist

Hello,

We're using BI 7.0 in my dept. I have a Data Store Object that I want to connect with a transformation to my DataSource. All objects are BI 7.0 objects, not 3.x. I right click my DataSource and select "create transformation" - as described in the BI documentation. I enter my DSO object as destination in the pop-up. As soon as I click on "execute" to confirm all entries in the pop-up, I get the error message "transformation does not exist, see long text". In the long text I find "The transformation specified by transformation ID , source and target , does not exist.". Well - of course my transformation doesn't exist yet, I wanted to create it! Does anyone share my unfortunate experience and found a way out?

Thanks for any tips you can give me! Annette