Error while doing ItemAdded option - System.ArgumentException and 0x80070057

HI,

I have a team site.

I have a custom list. In the Item Added event, I am getting the error in the ULS Logs as :

1) System.ArgumentException: Value does not fall within the expected range.  

 at Microsoft.SharePoint.Library.SPRequestInternalClass.AddOrUpdateItem.

2) <nativehr>0x80070057</nativehr><nativestack></nativestack>

I have the used the code as below in the Item Added event:

 public override void ItemAdded(SPItemEventProperties properties)
        {
           SPListItem currentItem = properties.ListItem;
           SPQuery testQuery = new SPQuery();
           SPList testList = null;
           SPListItem testItem = null;

           SPWeb currentSite = properties.Web;
 if (currentSite != null)
 {
testList = currentSite.Lists.TryGetList("Test List");
}         
if (testList != null)
           {
testQuery.Query = "<Where><Eq><FieldRef Name=\"TestStatus\" /><Value Type=\"Text\">Progress</Value></Eq></Where>";

SPListItemCollection nextItemCollection = testList.GetItems(testQuery);
                   
int CountItems = nextItemCollection.Count;

if (CountItems >= 1)
{
testItem = nextItemCollection[0];

currentItem["Title"] = testItem["Title"];
currentItem.Update();

testItem["TestStatus"] = "Done";
testItem.Update();
}
  } 
}

I have verified that the columns exist in the list. 60% of the time the code works, 40% of the time the code errors out.

What am I missing?

Thanks