I am trying to create some custom weldment profiles in SolidWorks.

I create the sketch, but then, when I am trying to save it as "Lib Feat Part" .(*sldlfp) I always receive the same message:
"This library feature part may contain features that are not related to selected features.
Do you want to create a simplified library feature part that does not include unrelated features? Please note that this may cause rebuild errors in this library feature part.
Yes / No"
Whatever is my answer, then, when trying to use the profile, I get the message "Library Feature is empty.", and I cannot use it...
Can someone explain me what am I doing wrong?