Import Solution - Plugin Assembly Error

Can someone help me to identify why the solution is throwing this error when I try to import the Plugin Assembly?

<?xml version="1.0"?>

<?mso-application progid="Excel.Sheet"?>

-<Workbook xmlns:html="www.w3.org/.../REC-html40" xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet" xmlns:x="urn:schemas-microsoft-com:office:excel" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns="urn:schemas-microsoft-com:office:spreadsheet">

<DocumentProperties xmlns="urn:schemas-microsoft-com:office:office"/>

-<ExcelWorkbook xmlns="urn:schemas-microsoft-com:office:excel">

<ActiveSheet>0</ActiveSheet>

<ProtectStructure>False</ProtectStructure>

<ProtectWindows>False</ProtectWindows>

</ExcelWorkbook>