Recently I faced this issue that when I try to deploy my WebPart.
Unable to add selected web part(s).
WebPartName: Cannon unregister UpdatePanel with ID ‘ctl00RTMPanel’ since it was not registerd with the ScripManager. This might occure if the UpdatePanel was removed from the control tree and later added again, which is not supported.
Parameter name: updatePanel.
I faced this issue twice and both the time the issue was not what display here. This could be sure to any error in the WebPart. Following are list resolution from multiple instances.
1. Check the WebPartName.webpart file.
Check whether you have a proper PublicKeyToken value. When I face the issue the value was PublicKeyToken=$PublicKeyToken$.
If you have used WSP builder then in the Visual Studio you will find this file at \WebPartsProject\12\TEMPLATE\FEATURES\WebPartName\WebPartName.webpart.
Sometime when you create a new WebPart using WSP builder then you do not get the correct value. The WebPartName.webpart file looks like below. I have changed our PublicKeyToken to a sample key.
<?xml version="1.0" encoding="utf-8" ?>
<type name="NamespaceName.WebPartName, WebPartName, Version=126.96.36.199, Culture=neutral, PublicKeyToken=99a999999d999999" />
<importErrorMessage>Cannot import WebPartName Web Part.</importErrorMessage>
<property name="Title" type="string">WebPartName</property>
<property name="Description" type="string">web part for organizational chart.</property>
2. Name of the WebPart should match the folder name. I mean if your WebPart name is WebPartName then the folder at \WebPartsProject\12\TEMPLATE\FEATURES\WebPartName should match to WebPartName.
3. Check you are getting proper data returned from your data provider and you are not missing any field in the return data. I was deploying my employee directory WebPart while UserProfile and People search scope was not configured properly. Once I fixed this issue everything worked great.
TROUBLE SHOOTING TIPS:
In both instance what I did was to create a brand new WebPart and copy code from old to new. Not complete code but few methods at a time. This greately help in pin pointing the issue.