I have installed MicroStation® V8i on a machine where I have already had SIGMA. Now when I load SIGMA, the toolbar comes up blank.

If MicroStation ®V8i is installed after installing SIGMA, the toolbar will come up blank (i.e. no icons). Problem can be remedied by copying SIGMA.dll, which can be found in SIGMA folder, to the C:\Program Files\Bentley\MicroStation\mdlapps\icons folder. This is assuming that your MicroStation is installed in default location. If you have MicroStation® installed elsewhere, please adjust the above path accordingly (i.e. locate the mdlapps folder and if the folder named icons is not already in there, create a new icons folder and paste our dll within that icons folder).