I had the same error, but none of the suggestions above worked. In my case all I had to do was to change my connection string to this:
string connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + FilePath + ";Extended Properties="Excel 12.0;IMEX=1;"";
Note the Single Quote around the Extended Properties attribute (‘Excel 12.0;IMEX=1;’). Once I added those single quotes the error disappeared!