It sounds like you have code in the constructor that probably should not be
there.

In the ComboBox_SelectedIndexChanged event procedure you can
Create a reference to frmMain using the modForms hashtable that I described
in my other response.

dim Fmain as form = modForms.Forms("frmMain")

You would have a friend or public function in FMain that takes one or more
parameters which indicate to the function what you need, and the function
will be written to return the data needed by your project form...as an
ArrayList, or whatever object serves your purposes.

Friend Function GetProjectData(ComboItem as String) as ArrayList
  dim ProjList as new ArrayList
  'Add code to get the data you need
  Return ProjList
End Function

Then you can call the function from your project form, get the return value,
and  handle the data from within the project form.

Don't try to manage your project form from within the main form...just get
the data you need using the function, and manage the data from within the
project form.