# JuMP Stopped Working Today

**URL:** <https://discourse.julialang.org/t/jump-stopped-working-today/46348>\
**Category:** Optimization (Mathematical)\
**Tags:** jump\
**Created:** [September 9, 2020, 9:35pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348 "2020-09-09T21:35:20Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![vattyamv](https://avatars.discourse-cdn.com/v4/letter/v/3bc359/32.png) [@vattyamv](https://discourse.julialang.org/u/vattyamv)\
**Post date:** [September 9, 2020, 9:35pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348/1 "2020-09-09T21:35:20Z")

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Hi, I’ve been using JuMP for a project and it stopped working today after I installed Gurobi. I get ERROR: LoadError: MethodError: no method matching Model(::Type{Gurobi.Optimizer}) when I set the solver to Gurobi, but it is also doing this for Ipopt. I have tried downgrading/upgrading the package versions but the same error keeps occurring. What could be causing this?

Thanks.

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [September 9, 2020, 10:20pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348/2 "2020-09-09T22:20:50Z")

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Try `] add JuMP@0.21`. You must have added another package that forced JuMP to downgrade.

Use a Pkg environment to avoid having incompatible versions of packages: [4. Working with Environments · Pkg.jl](https://julialang.github.io/Pkg.jl/v1/environments/)

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<div class="post-metadata">

**Author:** ![vattyamv](https://avatars.discourse-cdn.com/v4/letter/v/3bc359/32.png) [@vattyamv](https://discourse.julialang.org/u/vattyamv)\
**Post date:** [September 9, 2020, 10:34pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348/3 "2020-09-09T22:34:26Z")

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I tried that but it said no changes. My current packages are  
[c52e3926] Atom v0.12.21  
[2e9cd046] Gurobi v0.8.1  
[7073ff75] IJulia v1.21.3  
[b6b21f68] Ipopt v0.6.3  
[4076af6c] JuMP v0.21.3  
[e5e0dc1b] Juno v0.8.3  
[91a5bcdd] Plots v1.6.3  
[a759f4b9] TimerOutputs v0.5.6  
[fdbf4ff8] XLSX v0.7.3

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<div class="post-metadata">

**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [September 9, 2020, 10:45pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348/4 "2020-09-09T22:45:24Z")

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Close Julia and re-start. Everything looks okay. Not sure what the issue is.

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<div class="post-metadata">

**Author:** ![vattyamv](https://avatars.discourse-cdn.com/v4/letter/v/3bc359/32.png) [@vattyamv](https://discourse.julialang.org/u/vattyamv)\
**Post date:** [September 9, 2020, 11:07pm UTC](https://discourse.julialang.org/t/jump-stopped-working-today/46348/5 "2020-09-09T23:07:52Z")

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I restarted again and now it’s working for whatever reason. Thanks.