i get the following error

An entry with the same key already exists.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.ArgumentException: An entry with the same key already exists.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[ArgumentException: An entry with the same key already exists.] System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +52 System.Collections.Generic.SortedList`2.Add(TKey key, TValue value) +6152800 tswe.log.viewLog.InitControlItems() +1255 tswe.log.manager.OnInit(EventArgs e) +144 System.Web.UI.Control.InitRecursive(Control namingContainer) +140 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +480 

i cleared the logs from the server, didn't work, any idea why it happens?