It sounds like the walls have been drawn as existing and therefore locked, and it sounds like the user is trying to use Sketchup to edit the wall and not the PlusSpec Plugin & window editing tools. Cory, if you want to use Sketchup instead of the tools, you need to unlock the wall by right-clicking it and selecting unlock.
In some instances, a window was drawn in a previous version of PlusSpec, and Grant's answer is correct;
'Extensions > PlusSpec > Wall Tools > Redraw Walls (All)'
I can also recommend going to Extensions (at the top of Sketchup) >PlusSpec> Reset factory defaults
The correct way to remove or edit window types in PlusSpec, PlusDesignBuild or PlusArchitect is by using the following instruction.
1. Select wall the wall using the space bar
2. click the window icon in the PlusSpec toolbar
3. Click the remover:opening-remove:
4. Click on the window you want to remove.
NOTE: if you want to keep the opening but remove the window
1. Select wall the wall using the space bar
2. click the window icon in the PlusSpec toolbar

and choose

or right-click the wall and choose +Windows>edit window
3. Click the "none" icon on the bottom right of the window type selection
4. Click on the window you want to edit. The window is now removed, and the opening is still present.
Cory, video instructions are built into every PlusSpec version. Click on the orange question mark at the top of each tool dialog. This will get you up and running quicker.