We recently mentioned there appears to be a problem with Power Pivot in Excel 2010 when updating to Windows 10. It appears – although we have not been able to confirm it for ourselves yet – that the problem lies with the version of .NET (version 4.6), which is installed as part of the update. Apparently, .NET version 4.6 includes a new Just-In-Time (JIT) compiler for 64-bit processes, called RyuJIT, which is what is causing the current problem.For now, whilst a proper fix is being created, the quick workaround is apparently to disable RyuJIT via a registry key or by using PowerShell as follows:

• Registry key: Under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework add “useLegacyJit” DWORD with a value of 1;
• PowerShell: Set-ItemProperty -Path HKLM:\Software\Microsoft\.NETFramework -Name useLegacyJit -Type DWord -Value 1.

Hopefully, this resolves the problem for the interim.