Why does arcpy.mp.ArcGISProject() give an OSError?

[MatthewCallahan1]

I read the "Guidelines for arcpy.mp" doc, but when I call the sample code myself in the ArcGIS Pro Python window or from a Python script, I get this error:

import arcpy
aprx = arcpy.mp.ArcGISProject(r'C:\Path\To\Project\test_project.tbx')

Runtime error 
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "c:\program files\arcgis\pro\Resources\arcpy\arcpy\_mp.py", line 283, in __init__
    self._arc_object = arcgisscripting._mapping.ArcGISProject(*gp_fixargs((aprx_path,), True))
OSError: C:\Path\To\Project\test_project.tbx

Is this normal expected behavior?  The example code shows setting the project variable with an explicit .aprx file path, and I'm wondering why I'm unable to do the same on my machine.  The .aprx file is present/there are no misspellings in the file path in my code.  For reference, I'm running a fresh Windows 7 64-bit install with a fresh ArcGIS Desktop install as well (Pro v 1.4.1).

[DanPatterson_Retired · Accepted solution]

from the help topic why don't you reference the *.aprx, then you can get the toolbox as one of its properties.  You are referencing the toolbox (tbx) directly.

[MatthewCallahan1]

lol I'm dumb, that was it!  Time for bed, enough Python for today!

[KevinChristy1]

Dan, might you know why one would get this same exact error, but I am actually referencing the *aprx file?

[MichaelVolz]

Would you need to use Current in this circumstance?

[KevinChristy1]

Disregard, I realized that due to the nature that my project file and .aprx had the same name that I was omitting the project folder...Thanks though!

[ShraddhaSharma]

Hi Dan I am also facing the same problem but with my aprx file. 

[AllenDailey1]

I'm having the same error, but with my .aprx path, not with a toolbox path.  Have any of you been able to solve the problem?

Thanks!

[AllenDailey1]

I think I figured it out.  I haven't 100% tested this yet, but I believe the error resulted from the .aprx being Pro 3.0 while the machine I was running my script on had Pro 2.7, so it could not open or use the .aprx.  I am going to upgrade that machine to Pro 3.0 sometime this week.

Update:  it worked!

[Sean-Sweeney]

Thank you @AllenDailey1! Five minutes of Googling just saved me who knows how many hours of debugging.