cant loop cut after combining edges

I’m a beginner and try to get a floor plan for my tiny house done with Blender
and I use Blender 2.79 on Linux Mint 18 Acer Notebook.

After creating a plane, I loop cut to get some walls placed.
With the F key I combine edges (for later measurment with measureit) but after combining the edges I’m not able to loop cut any more.

A guy in another forum mentioned to
Could not find any solution. Sorry for bothering.

thank you!

What do you mean by combining edges with F key ?

Go and actually check your model for things like floating edges, duplicate faces, internal faces, duplicate vertices etc
Why have you not supplied a link to your .blend file ? This is mandatory for all support questions. Otherwise we cannot check any of this for you