Problem using same instance of indexSearcher for multiple requests

Try something like the following:

protected static IndexSearcher searcher = null;
...

if (searcher == null)
{
    searcher = new IndexSearcher(jobIndexFolderPath);
}

I also have a web application that uses the Lucene API to query (my web app does not writes on the index) and I create a new instance of the searcher for every request. It might not be very "performant" but I never had that kind of problem.

If you'd like, my web app is on Google Code so you can download the source code and take a look at what I did. Here's the url to the project http://code.google.com/p/goomez/

First of all it's not safe at all, it should be:

var searcher = (IndexSearcher)HttpRuntime.Cache["IndexSearcher"];
if(searcher == null)
{
     searcher = new IndexSearcher(jobIndexFolderPath);
     HttpRuntime.Cache["IndexSearcher"] = searcher;
}

In your code cache can expire between check and assignment