After contacting Atlassian support i found that i need to remove some configuration from my database.
They provided a workaround and it worked like a magic for me.
Unable to decrypt persisted value (SPCONTEXT: Current User: XXXXXXXX\XXXXXXXX, Current Web Application: SharePoint - XXXXXXXX.XXXXXXXX.com80, Current URL: http://XXXXXXXX.XXXXXXXX.com/_layouts/Atlassian/ConfluenceSettings.aspx, User Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; InfoPath.3; .NET4.0E; MS-RTC EA 2)): System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Web.HttpException: Unable to validate data. at System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean fEncrypt, Byte buf, Byte modifier, Int32 start, Int32 length, IVType ivType, Boolean useValidationSymAlgo, Boolean signData) at System.Web.... 1d1794ff-3a39-4aac-8221-1a2cb8ef2975
Configuration.MachineKeySection.EncryptOrDecryptData(Boolean fEncrypt, Byte buf, Byte modifier, Int32 start, Int32 length) --- End of inner exception stack trace --- at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture) at Atlassian.Confluence.SharePoint.MachineKeyWrapper.EncryptOrDecryptData(Boolean encrypting, Byte data, Byte mod, Int32 index,... 1d1794ff-3a39-4aac-8221-1a2cb8ef2975
at Atlassian.Confluence.EncryptionHelper.Decrypt(String encryptedValue) at Atlassian.Confluence.SharePoint.Version2010.Services.SitePropertyPersister.Decrypt(String encryptedValue) 1d1794ff-3a39-4aac-8221-1a2cb8ef2975
We have created a command-line utility that you may use on your SharePoint server to remove the Confluence configuration stored against a specific site. To remove the configuration from the site, follow these steps.
1. Log on to your SharePoint server with a user account that has Site Collection administration privileges for the site you wish to clear.
2. Download the utilty from http://www.atlassian.com/software/sharepoint/downloads/binary/DeleteConfluenceConfiguration.zip.
3. Open the zip file and extract the enclosed DeleteConfluenceConfiguration.exe file to a folder on your local disk.
4. Open a command prompt window and then change directory to the folder containing the executable.
5. Run the DeleteConfluenceConfiguration.exe utility, specifying the URL of the site that you wish to remove the Confluence configuration from. For example, if the site is 'http://sharepoint-server/sites/mysitecollection/subsite', then the command would look like this:
C:\Users\Administrator\Desktop> DeleteConfluenceConfiguration http://sharepoint-server/sites/mysitecollection/subsite
6. After running the utlity, you should see a success message. If you notice any messages containing an '[ERROR]' line, then it is likely that the settings were not deleted properly. In this case, you should contact Atlassian support directly for assistance.
Hope it will help others.
Best Regards :)