It is usually enough to restart the application. Since you are unable to reach the Site Manager with this error, you can do that an alternative way: by making a small change in your web.config file (it can be a 1 character space somewhere). Afterwards, your site will be restarted and should be up and running.
Please see the following detailed error message to check if this article applies to you:
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.
Parser Error Message: Thread was being aborted.
Source Error:
Line 62: <providers>
Line 63: <clear />
Line 64: <add name="CMSRoleProvider" type="CMS.MembershipProvider.CMSRoleProvider" connectionStringName="CMSConnectionString" applicationName="SampleApplication" writeExceptionsToEventLog="false" />
Line 65: </providers>
Line 66: </roleManager>
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