please help sed: -e expression #1, char 1: unknown command: `''

[方红霞]

please help
      i get a error message when i run below command
sed 's/cccc/dddd/g' -i aaa.txt
on sed 4.2.2 x64.exe.
the error message is:

error: sed: -e expression #1, char 1: unknown command: `''

but i run the command on sed (built 12/24/01) .exe X86 is ok!