EXCLUSIVE

"Melrose Place" star Jamie Luner will not face charges for the alleged sexual assault she was accused of committing on a then-16-year-old boy ... TMZ has learned.

The L.A. County District Attorney's Office declined to file charges against Luner after Anthony Oliver filed a police report earlier this year claiming she sexually assaulted him at a house party nearly 20 years ago.

Prosecutors cited a few reasons for refusing to move forward with the case, including ... Oliver's late reporting (more than 19 years), Oliver's credibility problems, lack of corroborating evidence and the bare facts as presented.

The credibility issue has to do with the story TMZ broke ... that Oliver had already been flagged by the court system for filing a crap ton of lawsuits, at least 22 over the past several years. He insists the suits were actually filed by his brother, and not himself.