Hi Schemer,

Can you provide the full stack trace of this exception? This will reveal
much important information of the failure.

Based on the error message, this exception is most likely of type
SecurityException, which is thrown by .Net Code Access Security engine. The
Net SecurityException is most likely caused by running the application
from a partial trusted location, because CLR will give limited permission
to partial trusted location running application. So, can you provide more
context information of your problem and application? For example, where do
you launch the application, local folder or network share?

It is strange that your application throws SecurityException while
constructing DirectoryInfo for current folder ".", because I have created a
little sample project which calls DirectoryInfo di = new
DirectoryInfo("."). Then I placed this test assembly in a network share
folder and no SecurityException will generate in the test. So, I recommend
you provide more detailed information to help me reproduce the problem.
This will be more efficient to reduce the troubleshooting time. Thanks.

Finally, setting FileIOPermission.AllLocalFiles property to
FileIOPermissionAccess.Read does not mean that it will give file read I/O
permission to all local files. But, it means that you want to check your
application's file read I/O permission to all local files. To explicitly
test this, you should use FileIOPermission.Demand method to force the .Net
runtime security checking. Actually, if this property can be used to grant
FileIOPermission to an application, this will become a big security hole,
because any untrusted application can use this property to acquire
FileIOPermission, which workarounds the .Net CAS engine.

Additionally, there is an easy to understand .Net CAS article in
codeproject, it will provide more useful .Net CAS background information to
you:
"Understanding .NET Code Access Security"
http://www.codeproject.com/dotnet/UB_CAS_NET.asp

I look forward to your further information. Thanks

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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Do you happen to run this application from a network share?

Willy.

Thanks for the replies.

Unfortunately, I have been unable to reproduce the problem since re-starting
the computer.
I removed references to FileIOPermission.  Instead, I create my input
FileStream as
   new FileStream(fn, FileMode.Open, FileAccess.Read, FileShare.Read);
and my output stream as either
   fsOut = File.Open(fnOut, FileMode.Append);
or
   fsOut = File.Open(fnOut, FileMode.Create);

Does the Security tab in the project's options have anything to do with
runtime issues, or just deployment?

Thanks again for the help.

"Schemer" <jumper@nospam.n