I have seen the issues several times where date/time parameters used to filter date in SSRS reports are switched to en-US despite the language of the reports is set to en-GB. If dates like 24/12/2015 or 15/12/2015 are picked , the report fails to load due to invalid date format.
I came across the article that describes a fix.
Hard code the UICulture value in RSViewerPage.aspx, found in
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\TEMPLATE\LAYOUTS\ReportServer
The modified code will look like:
<%@ Page language=”C#” Codebehind=”RSViewerPage.aspx.cs” AutoEventWireup=”false” Inherits=”Microsoft.ReportingServices.SharePoint.UI.RSViewerPage,Microsoft.ReportingServices.SharePoint.UI.ServerPages,Version=184.108.40.206,Culture=neutral,PublicKeyToken=89845dcd8080cc91″ UICulture=”en-GB” %>
Changing the UICulture causes lost the formatting of the sidebar on report viewer because the style folder is missing.
EN-GB has a locale ID of 2057, previously the page source was referring to 1033 which is “English (United States)”. The Styles subfolder which contains styles for each locale is on path.
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\LAYOUTS\ReportServer\styles
Create a new folder 2057 and copy all contents of 1033 into 2057.
Hard coding values is not recommended but has worked for the clients where I have implemented same change.
The Cumulative update 5 for SQL Server 2012 might fix the issue but did not manage to get it working.