Error opening .stp files – "File extension does not match file type"

[m_mackowiak4]

Hi everyone,

I'm having trouble opening certain .stp files. Every time I try to open them, I get the error: "Cannot open the file. The file extension does not match the file type."

Key observations:

New files work: If I create and save a new file myself, it opens without any issues.

Problematic files: The error only occurs with specific files (e.g., from external sources).

Troubleshooting: I've tried restarting the software and renaming the extensions (.stp / .step), but nothing helps.

I have attached two files to this post:

WorkingSample.stp – A file I created that opens fine.

Broken_Sample.stp – The file that triggers the error.

Could someone please check if the "broken" file opens for you or tell me what might be wrong with its header/format?

[CCarreiras]

Hi!

I'm not having any trouble opening Step_Broken:

What Inv. version are you using?

File attached, (Inv 26)

[m_mackowiak4]

I am using Autodesk Inventor 2017 (Build 256, Release 2017.4 Update)

[m_mackowiak4]

Interestingly, the same file opens without any issues on a different computer, which suggests the problem might be related to my local settings or software configuration.

[CCarreiras]

Check if you have space available in disk c:

Check if you have write permissions in the folder where is the step file.

Try the file attached...

[m_mackowiak4]

Thank you for providing the STEP file, but unfortunately, I am still unable to open it.

I have checked my C: drive, and I have over 40GB of free space. I also moved the file to my Desktop to ensure I have full write permissions.

When I try to open the file in Inventor 2018:

I select the **"STEP Files (*.stp, .ste, .step)" filter.

Even after selecting the file, the "Options" button remains greyed out.

If I try to proceed, I still get the same error: "The file extension does not match the file type."

[m_mackowiak4]

Inventor 2017*

[CCarreiras · Accepted solution]

Well.... is hard to say...
Restart your Pc and Inventor. Probably the step translator doesnt start properly in the previous start.

Also, I would Reset Inventor to try to fix something.

[m_mackowiak4]

I tried the Inventor Reset Utility and restarted my PC, but it still doesn't work.

[jnowel · Accepted solution]

Since AP203 version didn't work, might as well test AP214 (your working sample is AP214)
If that didn't work, you might as well try other CAD formats (Parasolid/IGES/SAT)

[m_mackowiak4 · Accepted solution]

Thank you for the suggestion, but as a Helpdesk technician, I need to resolve this specifically for .STP files. My client receives models in this format from multiple sources, so converting every file to IGES or SAT isn't a viable long-term solution. I need to fix the Inventor/Windows environment so the STEP Translator works natively.

[hollypapp65 · Accepted solution]

Something wrong with the brokensample.  Either IV2017 has a bug for AP242.  Or someone edited the file.

Version is 442 in the brokensample:

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[SBix26 · Accepted solution]

Definitely something not right with your computer-- it opens without a problem on my computer with Inventor 2017.4.13 (latest version).

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Sam B

Inventor Pro 2027 RTM | Windows 11 Home 25H2

[m_mackowiak4]

Thanks for your help and attention. The issue was caused by the directories in Public Documents/Inventor 2017. Some files were crashing when opening .stp files. I reinstalled Inventor 2017, copied some files from the old installation, and now it works.