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I'm sorry to hear about your situation. Yes, unfortunately there are some "exemptions". Now it's not "certain organizations" but rather governmental organizations that enjoy protections of "sovereign immunity" which is essentially a doctrine that says that the government is immune from lawsuit unless the government allows itself to be sued. The government, after all, makes the laws, and until it allows itself to be sued, it can't successfully be sued. The VA is a governmental agency, and as such the law has to specifically state that they can be sued. The Federal Tort Claims Act (FTCA) generally allows an aggrieved individual to bring a lawsuit against the Federal government for torts (bad acts) committed by the government or a governmental actor. But there are very specific exceptions. The FTCA provides:
The provisions of this chapter and section 1346(b) of this title shall not apply to. . . . (h) Any claim arising out of assault, battery, false imprisonment, false arrest, malicious prosecution, abuse of process, libel, slander, misrepresentation, deceit, or interference with contract rights.
So in short, the FTCA (which otherwise would authorize a lawsuit based on defamation) states that it does not apply to defamation lawsuits, and as such you can't successfully sue a governmental entity for defamation (libel is written defamation, slander is oral defamation).
I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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Thank you, ***** ***** luck to you!