I have created two user-defined functions, inv(targetCell) and
RevInv(targetCell, angleCell). The trigonometric function inv(theta) =
tan(theta) - theta, and there is no explicit function for the reverse. I
wrote a macro that uses Solver to find the angle that sets the targetCell to
zero. Here is the code and the formulae for the inputs:

Function RevInv(targetCell, angleCell)
SolverOptions MaxTime:=100, Iterations:=1000, Precision:=0.000001,
AssumeLinear _
:=False, StepThru:=False, Estimates:=1, Derivatives:=1,
SearchOption:=1, _
IntTolerance:=5, Scaling:=False, Convergence:=0.0001,
AssumeNonNeg:=False
SolverOk SetCell:="$H$10", MaxMinVal:=3, ValueOf:="0", ByChange:="$I$10"
SolverSolve (False)
End Function

targetCell: =G10-inv(I10)
angleCell: some arbitrary initial value (usu. 0.2)
cell that calls RevInv: '=RevInv(H10,I10)

So you can see that I am calling a user-defined function from the solver
within my other user-defined function. When I test the solver code in a test
macro with the same cells, everything runs perfectly. When I try to use the
"RevInv" function, I get the error message: "Solver: An unexpected internal
error occurred, or available memory was exhausted."

Does anyone have any idea what's going on? I guess I could run it as a
macro, but I want to be able to use this anywhere.

Thanks for your help,
Pflugs