Layout specification is missing error.

I’ve managed to do something to my NGClient solution, how I don’t know, but it is now displaying this error for frmMain:

Layout specification is missing: "null-null" frmMain.frm /OperaAccountView/forms OperaAccountView/forms/frmMain.frm Missing Spec

In the Outline view one of the Bootstrap rows appears to have forgotten what it is:

However looking at it in the .frm file it seems to be the same as the other rows:

customProperties : "attributes:{\
class:\"row\"\
},\
properties:{\
packagename:\"12grid\",\
specname:\"row\"\
}"

Any idea how to fix this/

I remembered that there is the ability to restore an earlier version of the form from local history, so I did that. Scary though.