To enable ASP.net support for your domain from Plesk please follow the following steps:-
1) Login to Plesk control panel.
2) Click on ASP.NET Settings.
3) When you open the ASP.NET configuration page for the first time, sample connection
parameters with common constructions are displayed. You can then delete them and
specify your own strings.
a) To add a string, enter the required data into the Name and Connection Parameters
input fields and click next to them.
b) To remove a string, click 
next to it.
4) Set up custom error messages that will be returned by ASP.NET applications in the
Custom Error Settings field:
A) To set the custom error messages mode, select an appropriate option from the
Custom error mode menu.
a) On - custom error messages are enabled.
b) Off - custom error messages are disabled and detailed errors are to be shown.
c) RemoteOnly - custom error messages are displayed only to remote clients, and
ASP.NET errors are shown to the local host.
B) To add a new custom error message (which will be applied unless the Off mode was
selected), enter the values in the Status Code and Redirect URL fields, and click 
.
a) Status Code defines the HTTP status code resulting in redirection to the error
page.
b) Redirect URL defines the web address of the error page presenting information
about the error to the client.
C) To remove a custom error message from the list, click next to it.
5) Configure encoding settings for ASP.NET applications in the Globalization Settings section:
a) To set an adopted encoding of all incoming requests, enter an encoding value into the
Request encoding field.
b) To set an adopted encoding of all responses, enter an encoding value into the
Response encoding field.
c) To set an encoding which must be used by default for parsing of the files, enter an
encoding value into the File encoding field.
d) To set a culture which must be used by default for processing incoming web requests,
select an appropriate item from the Culture list.
e) To set a culture which must be used by default when processing searches for a
locale-dependent resource, select an appropriate item from the UI Culture list.
6) Set a code access security trust level for ASP.NET applications in the Code Access
Security field.
7) Set client session parameters in the Session Settings field:-
a) To set up the default authentication mode for applications, select an appropriate item
from the Authentication mode list. Windows authentication mode should be selected
if any form of IIS authentication is used.
b) To set up time that a session can idle before it is abandoned, enter appropriate
number minutes into the Session timeout field.
8) Click OK to apply all changes.
