Error 500.19 The configuration section 'oracle.manageddataaccess.client' cannot be read because it is missing a section declaration

To use <oracle.manageddataaccess.client> element in web.config, it is necessary to register it with <section> or <sectionGroup> element inside <configSections>. You should uncomment this part because in your example it still commented:

<section name="oracle.manageddataaccess.client"          type="OracleInternal.Common.ODPMSectionHandler, Oracle.ManagedDataAccess, Version=4.122.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342" />

If uncommenting that line still not working, change it to <sectionGroup> element:

<sectionGroup name="oracle.manageddataaccess.client"               type="OracleInternal.Common.ODPMSectionHandler, Oracle.ManagedDataAccess, Version=4.122.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342" />

Also make sure that ODP Managed Data Access is already registered as assembly reference in your project and/or GAC (Global Assembly Cache).

I find it easier to manage the connection strings myself, instead of accepting Oracle's edit of the web.config file.

Comment out the <oracle.manageddataaccess.client> and corresponding <configSections> entry that oracle inserts.

Instead, I use the Microsoft <connectionStrings> section that can be accessed by the ConfigurationManager

<connectionStrings> <clear/> <add name="DB_CONN_STRING" connectionString="Data Source=servername:1521/dbinstancename;User ID=user;Password=pwd;"/> </connectionStrings>

Then in code, create my connection with:

using System.Configuration;using Oracle.ManagedDataAccess.Client;string conString = ConfigurationManager.ConnectionStrings["DB_CONN_STRING"].ConnectionString;OracleConnection myConnection = new OracleConnection(conString);myConnection.Open();

Instead of editing your web.config file manually you can also use application OraProvCfg.exe. Execute script like below (pick the version which is installed on your system):

set Oracle_x64=c:\oracle\product\12.1\Client_x64\odp.netset Oracle_x86=c:\oracle\product\12.1\Client_x86\odp.netset OraProvCfg_x64=%Oracle_x64%\bin\4\OraProvCfg.exeset OraProvCfg_x86=%Oracle_x86%\bin\4\OraProvCfg.exeset TNS_ADMIN=C:\oracle\network\adminset CONFIGFILE_PATH=.../web.configREM Delete configuration, if needed"OraProvCfg_x64" /action:unconfig /product:odpm /frameworkversion:v4.0.30319 /configfile:%$CONFIGFILE_PATH%"OraProvCfg_x86" /action:unconfig /product:odpm /frameworkversion:v4.0.30319 /configfile:%$CONFIGFILE_PATH%REM Add configuration"%OraProvCfg_x64%" /action:gac /providerpath:%Oracle_x64%\managed\common\Oracle.ManagedDataAccess.dll"%OraProvCfg_x64%" /action:gac /providerpath:%Oracle_x64%\managed\PublisherPolicy\4\Policy.4.121.Oracle.ManagedDataAccess.dll"%OraProvCfg_x64%" /action:gac /providerpath:%Oracle_x64%\managed\PublisherPolicy\4\Policy.4.122.Oracle.ManagedDataAccess.dll"%OraProvCfg_x64%" /action:config /configfile:%$CONFIGFILE_PATH% /product:odpm /frameworkversion:v4.0.30319 /providerpath:%Oracle_x64%\managed\common\Oracle.ManagedDataAccess.dll /set:settings\TNS_ADMIN:%TNS_ADMIN%"%OraProvCfg_x86%" /action:config /configfile:%$CONFIGFILE_PATH% /product:odpm /frameworkversion:v4.0.30319 /providerpath:%Oracle_x86%\managed\common\Oracle.ManagedDataAccess.dll /set:settings\TNS_ADMIN:%TNS_ADMIN%

If you skip /configfile:... then the application modifies the global machine.config file. Perhaps you also have to configure /product:aspnet, run OraProvCfg.exe and check the printout.

Oracle Providers for .NET Configuration Utility for .NET Framework 4 : Release 4.122.1.0 Production on Do Okt 18 09:00:41 2018Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.Usage:OraProvCfg  /action:<action>            [/force]            [/configfile:<app/web.config file path]            [/product:<product>]            [/component:<component name>]            [/productversion:<product version>]            [/frameworkversion:<.NET version>]            [/providerpath:<provider path>]            [/verbose:<verbose>]            [/log:<log file path>]            [/set:[*\]<section name>\<attribute name>:<attribute value>]            [/unset:[*\]<section name>\<attribute name>:<attribute value>]            <action>          = gac | ungac | register | unregister |                                config | unconfig            <configfile>      = complete file path of app/web.config                                for configuring/ unconfiguring odp/odpm/ASP.net entries only.            <product>         = odp | odpm | aspnet            <component name>  = oraclepermission | perfcounter |                                dbproviderfactory                                (for odp or odpm only)                              = all (default) | membership | profile | sitemap                                | rolemanager | personalization | webevent |                                a combination (i.e. "membership|profile")                                (for aspnet only)            <product version> = 4 digit assembly version number of the product                                (i.e. 4.112.2.0)            <.NET version>    = .NET Framework version                                (i.e. v2.0.50727 or v4.0.30319)            <provider path>   = full path location of the .NET assembly,                                including the the assembly file name                                (i.e. c:\OH\odp.net\bin\4\Oracle.DataAccess.dll)            <verbose>         = true (default) | false            <log file name>   = full path of the log file to log output            <section name>    = subsection name of oracle.manageddataaccess                                .client                                (e.g.)distributedTransaction            <attribute name>  = attribute name                                (e.g.)oramts_sess_txntimetolive            <attribute value> = attribute value (e.g.)240