I have a project which opens a simple Excel file and populates it. It was working fine until this morning, when it has suddenly started giving me the error above:
'Application' is ambiguous in the namespace 'Microsoft.Office.Interop.Excel'
Dim xl As Microsoft.Office.Interop.Excel.Application
Removing and re-adding the reference solved this issue. (David hasn't come back to allow me to mark his as the answer!)