ASP.NET Core blazor app, 404 blazor.server.js after .NET 10 installed

Question

I have a big project that uses Blazor, suddenly when I run it, the Blazor pages do not work anymore, because the blazor.server.js returns 404. This happened after I installed latest version of VS 2026 with the RTM version of .NET 10.

Short story, even if I compile with VS 2022, when I run the program in a system where I have .NET 10 SDK, blazor.server.js returns 404. As soon as I uninstall VS 2026 and .NET 10, the Blazor pages start working again.

This was verified in three different systems, and it is reproducible, install VS 2026 -> 404 -> then remove VS 2026 -> everything works.

The project targets .NET 9, but having .NET 10 build system breaks something.

Funny story, I have at least one other .NET 9 based project with blazor that works even with .NET 10. I wonder what I need to change to have it working.

I know that .NET 10 changes the way in which blazor resources are served, but I really wonder why having .NET 10 breaks Blazor in .NET 9 based project.

Anyone else experienced that?

marc_s · Accepted Answer · 2025-11-14 15:17:05Z

2

Found the problem, the project has a Directory.Build.props that contains

<RollForward>LatestMajor</RollForward>

That actually move forward during execution to latest framework version, actually making it run with .NET 10. The solution is rolling forward only for latest patch.

<RollForward>LatestPatch</RollForward>

This solves the problem

edited Nov 14 at 15:17

marc_s

760k186 gold badges1.4k silver badges1.5k bronze badges

answered Nov 14 at 15:14

Alkampfer

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