Biztalk : Inconsistent duplicate module attribute

Microsoft.XLANGs.BaseTypes.BPELExportable': inconsistent duplicate module attribute

Recently, I got this error that prevented my project from compiling. I had no idea what could trigger such an error, so I googled a little bit and quickly found a solution here (in german). 

The reason is that two properties are in conflict : BPEL Compliance on the project (Project > Properties >  Configuration properties > Build > BPEL Compliance) is set to true AND "Module Exportable" is also set to true in your orchestration properties. Setting "Module Exportable" to false solves the problem.