I bet that instead of ...
SH4/Mods/OPCFv1.2_green_TMO/Data/Menu/Skins/American/Gui/Layout/OBSPeriscope_Mask_1024.dds
you have in the ini file for your obsscope ...
SH4/Mods/OPCFv1.2_green_TMO/Data/Menu/Skins/American/Gui/Layout/Periscope_Mask_1024.dds
This is a common mistake, and you must edit it to the top version. Check to see if you have the files in the folders indicated.
