The most well-known adaptation of the Carmilla story is a 1970 film titled "The Vampire Lovers" which stars:
* Ingrid Pitt as Carmilla Karnstein
* Peter Cushing as General von Spielsdorf
* Pippa Steel as Laura
* Michael Coles as Baron von Spielsdorf
It is possible you are thinking of a different adaptation, or there may be a more obscure film you're trying to remember.
Could you please provide more information about the film you're looking for?