# Strange error when using the FBDF solver

**URL:** <https://discourse.julialang.org/t/strange-error-when-using-the-fbdf-solver/136405>\
**Category:** General Usage\
**Tags:** question, package, ordinarydiffeq\
**Created:** [March 26, 2026, 12:02pm UTC](https://discourse.julialang.org/t/strange-error-when-using-the-fbdf-solver/136405 "2026-03-26T12:02:20Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [March 26, 2026, 12:02pm UTC](https://discourse.julialang.org/t/strange-error-when-using-the-fbdf-solver/136405/1 "2026-03-26T12:02:20Z")

</div>

When I run the following script [Tethers.jl/src/Tether\_06c.jl at main · ufechner7/Tethers.jl · GitHub](https://github.com/ufechner7/Tethers.jl/blob/main/src/Tether_06c.jl) on Windows with continues callbacks using the FBDF solver I get the following error:

```julia-auto
4
┌ Warning: `ODESystem(args...; kwargs...)` is deprecated. Use `System(args...; kwargs...) instead`.
│ caller = ip:0x0
└ @ Core :-1
Tether_06c: Error During Test at D:\a\Tethers.jl\Tethers.jl\test\runtests.jl:5
  Got exception outside of a @test
  Current interpolant only works between tprev and t
  Stacktrace:
    [1] error(s::String)
      @ Base .\error.jl:44
    [2] _change_t_via_interpolation!(integrator::OrdinaryDiffEqCore.ODEIntegrator{FBDF{5, 1, ADTypes.AutoForwardDiff{1, ForwardDiff.Tag{DiffEqBase.OrdinaryDiffEqTag, Float64}}, Nothing, NLNewton{Rational{Int64}, Rational{Int64}, Rational{Int64}, Nothing}, typeof(OrdinaryDiffEqCore.DEFAULT_PRECS), Val{:forward}(), true, nothing, Nothing, Nothing, typeof(OrdinaryDiffEqCore.trivial_limiter!)}, true, Vector{Float64}, Nothing, Float64, MTKParameters{Vector{Float64}, Vector{Float64}, Tuple{}, Tuple{}, Tuple{}, Tuple{}}, Float64, Float64, Float64, Float64, Vector{Vector{Float64}}, ODESolution{Float64, 2, Vector{Vector{Float64}}, Nothing, Nothing, Vector{Float64}, Vector{Vector{Vector{Float64}}}, Nothing, ODEProblem{Vector{Float64}, Tuple{Float64, Float64}, true, MTKParameters{Vector{Float64}, Vector{Float64}, Tuple{}, Tuple{}, Tuple{}, Tuple{}}, ODEFunction{true, SciMLBase.AutoSpecialize, FunctionWrappersWrappers.
...

```

Is that a bug in the solver or in my code? It works fine on Linux and Mac, it also works fine without the callbacks.

My current workaround: Use the `KenCarp4(autodiff=false)` solver. But it is much slower.

---

<div class="post-metadata">

**Author:** ![ChrisRackauckas](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/chrisrackauckas/32/77_2.png) [@ChrisRackauckas](https://discourse.julialang.org/u/ChrisRackauckas)\
**Post date:** [March 27, 2026, 12:58pm UTC](https://discourse.julialang.org/t/strange-error-when-using-the-fbdf-solver/136405/2 "2026-03-27T12:58:54Z")

</div>

That needs a reproducer. `_change_t_via_interpolation!` in a callback should only be triggering in the current interval.