I've deployed a report that uses a custom assembly which calls a web service
to return a specific string value.  The web service is running on the same
server as the web front end for Reporting Services, and works as expected
when called separately.  When I run the report the column that holds the web
service's return value instead shows an error message:
"Request for the permission of type 'System.Net.WebPermission, System,
Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed."

I've also got the stack trace, but I'm not sure that'll be helpful in this
context.  If it is, however, I'm happy to paste it in here.

The custom assembly is asserting that permission, with no luck.  I can
however retrieve that value if I set the Reporting Services web site's
web.config file to use FullTrust permissions instead of relying on the
rssrvpolicy.config file for permissions settings (replacing

"      <securityPolicy>
       <trustLevel name="RosettaSrv" policyFile="rssrvpolicy.config" />
     </securityPolicy>
   <trust level="RosettaSrv" originUrl="" />"

with

"      <securityPolicy>
       <trustLevel name="Full" policyFile="internal" />
     </securityPolicy>
   <trust level="Full" originUrl="" />")

That implies to me that I could set a more resrictive security policy in
rssrvpolicy.config and still be able to use my web service resource, if only
I knew what settings to use.  And, for what it's worth, if I access the
report on the web site on the sql server that's running this instance of
Reporting Services I see the exact same behavior (a WebPermissions failed
error when under the default web.config and success when using a completely
permissive web.config setting) with the web service itself running on a
remote machine (the machine that's hosting the web front end for reporting
services).  Also, FWIW, I've tried setting FullTrust on the custom assembly
in rssrvpolicy.config as well, and the custom assembly is installed in the
GAC, to boot.  That also has produced no joy.

Anybody have a tip to point me in the right direction of which permissions I
should set in rssrvpolicy.config to allow this behavior?

If it would be helpful I can also detail the web service's internals, though
it doesn't seem to be the source of the problem.  Short form: the web service
uses the SAP .Net Connector to access a long text field in the SAP database
and return its value for a given SAP object.  I can't do this directly in the
report because the SAP .Net Connector's assemblies are 32-bit .Net 1.1x
beasts and we're running on a 64-bit SQL Server box, thus the web service.