C# Exception: The process cannot access the file

i'm getting exception: process cannot access file.

here's snippet code:

if (!monitor.tryenter(lockobject))
    return;
try
{
    watcher.enableraisingevents = false;
    try
    {
        xmldocument xdoc = new xmldocument();
        xdoc.load(filename);
        xdoc = null;
    }
    catch (xmlexception xe)
    {
        using (streamwriter w = file.appendtext(filename))
        {
            console.writeline(xe);
            w.writeline("</test>");
            w.writeline("</testwrapper>");
        }
    }
    system.threading.thread.sleep(2000);
    xpathdocument myxpathdoc = new xpathdocument(new streamreader(filename, system.text.encoding.getencoding("windows-1256")));
    xslcompiledtransform myxsltrans = new xslcompiledtransform();
    myxsltrans.load("d:/gs/xsl/test.xsl");
    xmltextwriter mywriter = new xmltextwriter(destinationfile, null);
    mywriter.formatting = formatting.indented;
    mywriter.indentation = 4;
    myxsltrans.transform(myxpathdoc, null, mywriter);
    mywriter.close();
}
catch (exception e)
{
    console.writeline("the process failed: {0}", e.tostring());
}
finally
{
    monitor.exit(lockobject);
    watcher.enableraisingevents = true;
    gc.collect();
    gc.waitforpendingfinalizers();
    gc.collect();
}

the code working before added these lines. these testing if xml file without closing tags (which) add tags. after added following code started giving me exception.

try
{
    xmldocument xdoc = new xmldocument();
    xdoc.load(filename);
    xdoc = null;

}
catch (xmlexception xe)
{
    using (streamwriter w = file.appendtext(filename))
    {
        console.writeline(xe);
        w.writeline("</test>");
        w.writeline("</testwrapper>");
    }
}  

what wrong here ?

here error i'm getting :

the process failed: system.io.ioexception: process cannot access file 'z :\tf_b1bba.xml' because being used process. @ system.io.__error.winioerror(int32 errorcode, string maybefullpath) @ system.io.filestream.init(string path, filemode mode, fileaccess access, nt32 rights, boolean userights, fileshare share, int32 buffersize, fileoptions o ptions, security_attributes secattrs, string msgpath, boolean bfromproxy, boolea n uselongpath) @ system.io.filestream..ctor(string path, filemode mode, fileaccess access, fileshare share, int32 buffersize) @ system.xml.xmldownloadmanager.getstream(uri uri, icredentials credentials, iwebproxy proxy, requestcachepolicy cachepolicy) @ system.xml.xmlurlresolver.getentity(uri absoluteuri, string role, type ofo bjecttoreturn) @ system.xml.xmltextreaderimpl.openurldelegate(object xmlresolver) @ system.threading.compressedstack.runtrycode(object userdata) @ system.runtime.compilerservices.runtimehelpers.executecodewithguaranteedcl eanup(trycode code, cleanupcode backoutcode, object userdata) @ system.threading.compressedstack.run(compressedstack compressedstack, cont extcallback callback, object state) @ system.xml.xmltextreaderimpl.openurl() @ system.xml.xmltextreaderimpl.read() . @ system.xml.xmlloader.load(xmldocument doc, xmlreader reader, boolean prese vewhitespace) @ system.xml.xmldocument.load(xmlreader reader) @ system.xml.xmldocument.load(string filename) @ gselinterface.program.convert(object source, filesystemeventargs f) in c:\ documents , settings\administrator\desktop\consoleapplication1\consoleapplicat ion1\program.cs:line 178

may file opened in other thread? or program?

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