Conversation so far:
When did the film begin production?
The film went into production in 1991.
Where was it filmed?
CANNOTANSWER.
Who were the actors?
Julia Roberts, who agreed to play Viola.
Who else?
CANNOTANSWER.
Did she actually star in the film?
she withdrew from the film, six weeks before shooting was due to begin.

Question: Why did she withdraw?
Self-contained rewrite: Why did Julia Roberts withdraw from Shakespeare in Love?