Problem adding MIB to MibBrowser Free Tool

Hello,

I'm not sure what the problem is, but it seems like it should be pretty straight forward. I am trying to load a MIB, but I'm getting an error. Here is a description of the problem:

- I have downloaded the DOCSIS MIB definitions (DOCS-CABLE-DEVICE-MIB_RFC4639.mib) into ManageEngine/MibBrowser Free Tool/mibs

- then I open my ManageEngine MibBrowser Free Tool and click on 'File', then on 'Load MIB' and then point to 'DOCS-CABLE-DEVICE-MIB_RFC4639.mib'. Once I click on 'Open', I receive the following error:

Not a valid MIB file: C:/Program Files (x86)/ManageEngine/MibBrowser Free Tool/mibs/DOCS-CABLE-DEVICE-MIB_RFC4639.mib

Does anyone know why I'm getting this error?

Thanks in advance!