XML file for BSDF gives negative thickness

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Hi, I have generated a BSDF for shading by using genBSDF through a python code in grasshopper. When I import the file to LBL Window to extract SHGC and other thermal properties to report to BSDF-IDF format, the BSDF gives a negative thickness (i.e. -1.00) while the going through the xml file in text editor the thickness parameter is correct (i.e. 11 inches). This crashes the LBL Window if i try to calculate values. Any help would be greatly appreciated. Thank you.