Eraser tool 'jammed'and Interface discombobulated

[Ps2Gimp]

Can't do a simple erase. Bottom dialogue indicates the "active layer's pixels are locked".
Confusion finding adjustments, specially with my interface having gone Berzerk it seems.

So can someone please help wich ever first:

1. Reset the interface for a fresh start so i find tools easy. Re-install not fixing anything.
2- Set my eraser free...make it erase again.

Thanks