Abolhaggag Bashir 

Alright, let's clarify a few things from your post.

When I attempt to convert or open (.TMW) Translation Memories through TradosLegit, I encounter this error:

TradosLegit is not designed for converting TMW memories. It's primarily used for facilitating the segmentation of the file you're trying to convert into a TTX or a Bilingual DOC.  The error you're seeing is likely due to the absence of the complete translation memory in a folder.  You may only have the TMW file, or certainly not all the files needed.  These older translation memories are composed of 5 files, and you need all of them:
* tmw
*.iix
*.mdf
*.mtf
*.mwf

I'm unsure of the issue. I can't seem to convert, import, upgrade, or even open legacy TM (.TMW). When I attempt to use Upgrade Translation Memories, I receive this message.

Now that we've clarified this, you should understand why it's not working!  However, I am aware that is actually a problem that needs to be fixed anyway as even if you have all 5 files the current version of the "Trados Compatibility and Migration Power Pack" fails to convert and you will see an error message (a different one):

If you're desperate, send me the translation memory (all 5 files) and I'll convert it for you with an older version of Studio, or even with Translators Workbench.  You can zip them and attach to this thread, or if the TM is provate email the zip to me pfilkin at sdl dot com

 Abolhaggag Bashir 

Alright, let's clarify a few things from your post.

When I attempt to convert or open (.TMW) Translation Memories through TradosLegit, I encounter this error:

TradosLegit is not designed for converting TMW memories. It's primarily used for facilitating the segmentation of the file you're trying to convert into a TTX or a Bilingual DOC.  The error you're seeing is likely due to the absence of the complete translation memory in a folder.  You may only have the TMW file, or certainly not all the files needed.  These older translation memories are composed of 5 files, and you need all of them:
* tmw
*.iix
*.mdf
*.mtf
*.mwf

I'm unsure of the issue. I can't seem to convert, import, upgrade, or even open legacy TM (.TMW). When I attempt to use Upgrade Translation Memories, I receive this message.

Now that we've clarified this, you should understand why it's not working!  However, I am aware that is actually a problem that needs to be fixed anyway as even if you have all 5 files the current version of the "Trados Compatibility and Migration Power Pack" fails to convert and you will see an error message (a different one):

If you're desperate, send me the translation memory (all 5 files) and I'll convert it for you with an older version of Studio, or even with Translators Workbench.  You can zip them and attach to this thread, or if the TM is provate email the zip to me pfilkin at sdl dot com

I am not "desperate". Thanks a lot for the offer. Much appreciated.