MSSIPOTF_E_FILETOOSMALL 0X8009700B Fix: Startup & Install Errors

First, what's happening?

That error code — MSSIPOTF_E_FILETOOSMALL — is Windows telling you that the digital signature on a file doesn't match its content. It literally means the file is too small to contain the last table in its signature structure. In plain English: the file is either truncated, corrupted during download, or a program is trying to run a signed file that got mangled.

I've seen this mostly with installer files (like setup.exe from a download manager) and occasionally with driver updates. The real trigger is often a dropped connection that saved a partial file, or a disk that's running out of space mid-write.

Here's the good news: you don't need to reinstall Windows. Work through these fixes in order — most people stop at step one.

Fix 1: The 30-second fix — re-download the file

You won't believe how often this solves it. The original download is just bad. Delete the file you tried to run (the one that gave the error) and grab it again. But don't just click the same link — clear your browser cache first so you don't pull the same corrupted copy.

1. Right-click the file and select Delete. Don't send it to the Recycle Bin if you can avoid it — shift+delete works.
2. Empty the Recycle Bin.
3. Clear your browser cache. In Chrome or Edge, press Ctrl+Shift+Delete, choose "All time", and check "Cached images and files".
4. Download the file again. If it's an installer, grab it directly from the vendor's site — not a mirror.
5. Try running it again.

If it works, you're done. If you still get 0X8009700B, move on.

Fix 2: The 5-minute fix — clear temp files and check disk space

This tripped me up the first time. Windows uses temp folders to cache parts of downloaded executables, and a stale temp file can cause signature checks to fail. Also, low disk space on your system drive can cause partial writes — even for files that already exist.

Clear temporary files

1. Press Windows + R, type %temp%, and hit Enter.
2. Select everything in that folder (Ctrl+A) and hit Delete. Some files will be in use — that's fine, just skip them.
3. Do the same for C:\Windows\Temp. You'll need admin rights; just approve the prompt.

Check disk space

Open File Explorer, click This PC, and look at the C: drive. If it's showing less than 500 MB free, you need to clear space. Run Disk Cleanup:

1. Search for "Disk Cleanup" in the Start menu and open it.
2. Select the system drive, let it scan, then check everything under "Files to delete".
3. Click OK and wait.

Now try your original file again. No luck? Then it's time for the advanced fix.

Fix 3: The advanced fix — dig into the signature chain

If re-downloading and cleaning temp files didn't work, something deeper is off. This usually points to a certificate trust issue on your machine — or the file itself is genuinely corrupted beyond repair.

Check the file's digital signature

Right-click the problematic file, go to Properties, then the Digital Signatures tab. You should see a list of signatures. If the tab is missing or says "The digital signature is not valid," that's your smoking gun.

If the signature shows as valid, then the problem isn't the file itself — it's the code that's calling it. That gets trickier, but let's try a few things.

Run a system file check and DISM

Corrupted system files can mess with how Windows validates signatures. Open an elevated Command Prompt (right-click Start, choose "Command Prompt (Admin)" or "Windows Terminal (Admin)"), then run:

sfc /scannow

Wait for that to finish. Then run:

DISM /Online /Cleanup-Image /RestoreHealth

This checks the system image for corruption. It can take 15–20 minutes, so give it time. After both complete, restart and try the file again.

Update your root certificates

Sometimes the error is because Windows doesn't trust the certificate chain anymore — especially if your system clock is wrong or you haven't installed updates for a while. Check the date and time first (right-click the clock, "Adjust date/time", ensure "Set time automatically" is on).

Then force a certificate update. In the Command Prompt, type:

certutil -generateSSTFromWU roots.sst

That pulls the latest root certificates from Windows Update. It won't install them, but if it errors out, you'll know your network is blocking updates. If it succeeds, it's not your certificates — it's the file itself.

Last resort: get a different version of the file

If you've done all this and the error persists, the file you're trying to run is simply bad. Maybe the vendor released a broken build. Look for a previous version or a different download link. For drivers, check the manufacturer's site for older releases. For installers, try the 64-bit instead of 32-bit (or vice versa).

Pro tip: If this happens with an MSI file, you can sometimes extract its contents without running it. Use msiexec /a "filename.msi" from an admin command prompt — this triggers an administrative install that ignores signature checks. But only do this if you trust the source completely.

Why does this even happen?

In my years on the help desk, I saw this most often after someone interrupted a download — maybe the browser froze, or the laptop went to sleep mid-download. Antivirus software occasionally quarantines part of a file too, which leaves the rest behind as a partial chunk. That's why re-downloading is so often the fix.

If you're pulling the file from a network share, also check the source — a corrupted file on the server will keep giving you the same error no matter how many times you copy it.

When to give up and call in support

If none of these steps cleared the error, and the file is critical for work, it's time to contact the vendor or your IT team. Have the error code ready — 0X8009700B — and mention that you've already tried re-downloading, cleared temp files, and run SFC/DISM. That saves everyone time.

But honestly, in most cases, Fix 1 solves it. Don't overthink this one. Get a clean download, and you're back in business.