Unable to cast object of type to'Microsoft.SharePoint.WebPartPages.WebPart'

Some of us face this issue while casting webparts in the page. Your code is like this when you get this error.

foreach (Microsoft.SharePoint.WebPartPages.WebPart item in wpManager.WebParts)
            {
                if (item.Title.Equals(webpartTitle))
                {
                    isExists = true;
                }

            }

Make like this

foreach (System.Web.UI.WebControls.WebParts.WebPart item in wpManager.WebParts)
            {
                if (item.Title.Equals(webpartTitle))
                {
                    isExists = true;
                }

            }