I am running Autocad 2012 and I tried to use the block swap command under the Express Tools. After selecting the block that I want to replace, I get an error stating that the block name contains an invalid character. The name contains invalid characters. The name is: DomeCamera_WallMount, but in the command bar it says object name:*U302. The * is what Autocad doesn't like.
*U302 indicates that the block is an unnamed, anonymous block. If you run the PURGE command you'll most likely be able to remove it. Do that and try your swap command again.
I agree with the other user that said this sounds like an embedded block issue. When all else fails with the blockreplace command, I just insert the new block into the one to replace then explode all instances of the old one. Voila.
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