I believe the problem is caused by the following two lines:
newdock.ID = WPID
" returns an ID which contains "-". By default you cannot use strings as IDs of ASP.NET controls that contain the "-" character. So the "-" character should be replaced with a "legal" ASP.NET character. Moreover the Guid can start with a numeric character, which once again is invalid. You should make sure the ID starts with alphabetic character. For an example this line of code should be used instead:
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