Andrew, attached is a similar spacer that I drew recently with CADX11 and imported into LCAM. Interesting to note, that I have four entities around the outside edge - when I loaded your file into LCAM the outside contained 257 entities - that was after cleaning and optimizing. My drawing is only 2" X 4" though.
Since I was able to load your file the number of entities should not have caused a problem for you, but the complexity did raise some questions.
Bob @ BobsShop