# Troubleshooting Connection Issue Between Oracle Database & Opkey July 6, 2018 Iffat Ara Khanam **Symptoms:** While connecting Opkey with the Oracle database, located on local or remote machine, Opkey users come across such issues: System.Configuration.ConfigurationErrorsException: An error occurred creating the configuration section handler for system.data: Column ‘InvariantName’ is constrained to be unique. Value ‘Oracle.DataAccess.Client’ is already present. **Cause:** The most common cause of such type of issue is installing or uninstalling of ODAC driver multiple times. **Resolution:** The resolution for the above cause is to remove one row from the machine.config file of Microsoft.Net folder. The machine.config file can be found at the following path: `C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config` The row to be deleted is given below: `` **_Note:_** _Check before row deletion: Please check that the row with the above given value exists twice in the machine.config file. Now remove the last row with these values._ Author Radhe Shyam Prajapati ### Iffat Ara Khanam Technical Content Lead [Go to this author's LinkedIn profile.](https://www.linkedin.com/in/iffat-ara-khanam-ba95012a1) Iffat is the content lead at Opkey. She has expertise in writing technical content focused around ERP testing, Cloud apps, automation and other IT related topics. She has rich experience in writing content for marketing collateral like whitepapers, case studies, newsletters etc. which helps in funnel creation for sales.