SSIS package fails with only OnPreValidate in logs when run from a .NET app

I've created a SSIS package which runs smoothly when launched from SQL Server Data Tools (I use SSDT 2015 with SQL Server 2005 Developer Edition on my PC), but fails with only the following line in logs when I run it from a .NET app:

Fields:event,computer,operator,source,sourceid,executionid,starttime,endtime,datacode,databytes,messageOnPreValidate,<my_computer>,<my_operator>,Test,{E7D40776-05B7-4D1D-8D78-8C87E722E596},{755AD039-B5B4-42B0-9ECA-E396054DEB2F},28.10.201614:44:06,28.10.201614:44:06,0,0x,

I use the following code to call the package from my .NET app (I just copied the SSIS package in the .NET project from SSIS project and specified it to be copied to the output directory so I could call it from the file system):

publicvoidExecute(string filePath,DateTime period){var pkg = app.LoadPackage(filePath,null);var variables = pkg.Variables;
    variables["Period"].Value= period;var pkgResults = pkg.Execute(null, variables,null,null,null);}

I've tried switching package protection level to DontSaveSensitiveData, but it didn't help.

What am I doing wrong? Is there a way to at least get some proper data about why the package is failing?