I got this error message( !laymgr.cpp@987:elockviolation) today after launching & opening file previously saved in AutoCade 2007 LT. I had work on Autocad three day ago and I did not encounter such problem. I remember that since then, I have installed software Defender Pro 2010 (DP). Therefore after a Uninstalling & reinstalling the AutoCad the problem was not solved. I decided to uninstall DP from my system. After rebooting my system, I launching Autocad, the error was gone and the program appeared to be working flawlessly. Problem is DP not AutoCad.
Conclusion: If anyone getting the above error, uninstall your Anti-Virus particularly DP 2010. DP has some thing to do with it.