creating blocks from a dwg

i have been given several cd's containing dwg's of hvac layouts, what i would like to do is create blocks from details in the dwg's. i am not sure i am going about it correctly. i do wblock, select objects, convert to blocks and set units to mm. it does create a block file but when i try and insert the block into a new drawing i get an error saying the block references its self? it does work if i change the block name in the insert window name box.

you get that error if what yu select already has the name of the file you are creating. When you WBLOCK, select block from the drop down to write out the blocks already defined.