Someone in the comments section of
this Temple of Schlock post suggests that the film was proposed as part of a series to be made by Gold Key Entertainment (the same as the comic books, I wonder?) but was never actually made. It has a listing on IMDb, but aside from three cast members (Price, Stephanie Beacham and Andrew Kier), no director, writer or crew is listed.
Here's a list of Gold Key's "Zodiac Features":
Curse of the Moonchild turns up in some old TV listings, but then the Oliver Reed title The Age of Pisces doesn't even show up on IMDb.