VBA help

I am not sure if this is the right place to raise this question, moderator may shift the topic if required.

I am using SET statement as below:

Set objBlockRef = ThisDrawing.ModelSpace.InsertBlock(varInsertionPoint, "D:\SADD1000S.dwg", dblX, dblY, dblZ, dblRotation)

When user clicks "Done" button on userform, program loads a predefined drawing and then inserts block from SADD1000S.dwg. Above command works fine when I click "Done" for the first time, but when I click "Done" again, program throws runtime error.

I believe that same is due the fact that SADD1000S.dwg is open in the background. Can anyone help me on how to close the SADD1000S.dwg file after using above SET statement?