Automation error

I need help...
When I try to start my application in ACAD2000, in some cases it doesn't
work. I am getting message: ; error: Automation Error. Object is not open
for write.
But, it works when I start new drawings, only in some imported drawings from
other companies it doesn't work.
I am using dll's to reach some external datas, and processing them with
operations in VLisp code.
How to solve problem?
Thanks in advance...
Sinisa