Iam trying to register in my site ,but when i click on registration link iam getting Error and in admin log i see the below exception

Message:The parameter 'username' must not contain commas. Parameter name: username

StackTrace:

at System.Web.Util.SecUtility.CheckParameter(String& param, Boolean checkForNull, Boolean checkIfEmpty, Boolean checkForCommas, Int32 maxSize, String paramName) at System.Web.Security.Membership.GetUser(String username, Boolean userIsOnline) at DotNetNuke.Security.Membership.AspNetMembershipProvider.GetMembershipUserCallBack(CacheItemArgs cacheItemArgs) at DotNetNuke.Common.Utilities.DataCache.GetCachedDataFromRuntimeCache(CacheItemArgs cacheItemArgs, CacheItemExpiredCallback cacheItemExpired).

how can i resolve this error .please help me