If you're using TurboTax Desktop, make sure your program is updated. You can do a Manual Update.
If this doesn't resolve the error, go back to your K-1 entry and enter $0 in Box R on the K1 and Report $23,000 on line 6a and $7500 on line 6c of the worksheet.
If you're using TurboTax Online, clear your Cache and Cookies and step through the section again.
Let us know if it doesn't resolve for you.
Here's more info on Entering a Solo 401K Contribution.
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