Can not import this web part

Question

dll is in the GAC. 
safe control is listed correctly.  Not sure why.  Code is listed below.  any help is appreciated.
using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
namespace VendorDropdown.VisualWebPart1
    [ToolboxItemAttribute(false)]
    public class VisualWebPart1 : WebPart
           // Visual Studio might automatically update this path when you change the Visual Web Part project item.
             private const string _ascxPath = @"~/_CONTROLTEMPLATES/VendorDropdown/VisualWebPart1/VisualWebPart1UserControl.ascx";
           String drpListSelected = "";
           DropDownList drpList = new DropDownList();
           protected override void CreateChildControls()
               Control control = Page.LoadControl(_ascxPath);
               SPSite site = SPContext.Current.Site;
               SPWeb web = SPContext.Current.Web;
               SPList list1 = web.Lists["Vendor"];
               var listitems = list1.Fields["Company"];
               drpList.DataSource = listitems;
               drpList.DataTextField = "Company";
               drpList.DataValueField = "ID";
               drpList.DataBind();
               Controls.Add(control);
               drpList.SelectedIndexChanged += new EventHandler(this.ddlAllLists_SelectedIndexChanged);
           void ddlAllLists_SelectedIndexChanged(object sender, EventArgs e)
               try
                   //set the selected value and logic
                   drpListSelected = drpList.SelectedValue;
                   this.Page.Response.Redirect("~/Lists/Vendor/DispFormVendor.aspx?iD="
+ drpListSelected);
               catch (Exception ex)
                   //  LogManger.WriteLog(" Error in EventCalendarWebPart.cs ddlAllLists_SelectedIndexChanged()" + ex.ToString());
        protected override void Render(HtmlTextWriter output)
          EnsureChildControls();
          base.RenderContents(output);

Answer 1

What is the exact steps you are following
Did you run the application as admin
Check below:
http://stackoverflow.com/questions/120928/sharepoint-error-cannot-import-web-part
Make sure web part is created in 64-bit system
http://sharepoint.stackexchange.com/questions/11820/custom-web-part-deployment-produces-cannot-import-this-webpart-error
Ensure your feature actually contains the correct version of webpart/assembly.
Ensure safecontrol is correctly defined with correct version
Now, Delete all your solution related webparts from the webpart gallery. (This is what really helped me). You can use a ps script for that.
Redeploy solution. (This will activate the features, but not add the webparts to webpart gallery).
Deactivate the webpart feature either via UI or Disable-SPFeature command (i used ps)
Activate the webpart feature (Enable-SPFeature). This will bring all the new updated webparts to the web part gallery.
Check below:
http://www.dotnetmafia.com/blogs/dotnettipoftheday/archive/2008/10/06/troubleshooting-cannot-import-web-part-error.aspx
http://social.msdn.microsoft.com/Forums/sharepoint/en-US/5f6d9e1a-315f-49ea-96d3-824edb642cd7/unable-to-add-selected-web-parts-cannot-import-this-web-part
f it is NOT the public key token problem (fully qualified assemby name) then try:
got to site settings -> webparts -> (If your webpart is in the list delete it) click on NEW -> check the webpart in the list, check overwrite, click on add to catalog.
If this helped you resolve your issue, please mark it Answered