Unable to select the transformation in a transport request

Solution

Most probably it will be because transformation is already contained in a TR, happens mostly when we give collection mode as automatic.

1. Double click on your transformation.

2. Go to Extras - Object Directory Entry

3. Then click on "Lock Overview"

4. It will display message saying "the object is not locked" or it will show you the transport in which it is already collected.  This helps in finding to which transport request its contained.