Unable to load “lpsolve55.dll” in VS2015 on 64-bits OS

Question

For a project I am working on, I need to solve a mathematical model. I chose to do this using Microsoft.Solver.Foundation and the SolverFoundation.Plugin.LpSolve plugin. Both associated .dll files for these extension seem to work fine, as VS2015 recognizes and references them without a problem and compiles and runs my program without errors.

This is however up untill I try to actually solve my optimization, which needs "lpsolve55.dll" to work. I have downloaded this dll and put it in my project's bin/Debug folder, but for some kind of reason VS2015 just doesn't recognize it. Ie

• I can't reference it by simply browsing to it from my "Add Reference" tab.
• It's impossible to (un-)register it via the regsvr32 cmd-prompt application, as it doesn't have any DLL (Un-)registry entry points.
• The TlbImp.exe cmd-prompt application can't handle it.

So basically, after discovering the above (after trying the most-common internet solutions), I still feel quite dissatisfied to get the error message while I try to solve the optimization -

Unable to load DLL 'lpsolve55.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

The wierd part is also that I have another project in which I solve a similar problem, where there are absolutely no problems at all using lpsolve55.dll....

Some quick facts:

• I reference .NET framwork 4.5.2. I have changed it to 4.5 as well as 4.0, but this didn't change anyting.
• For as far as I can tell, the bin/debug folder of my projects are identical.
• I am working on a fully updated windows 10 OS, 64 bits, while using visual studio 2015.

My question would thus be whether or not some of you have encountered a similar problem and if you were able to solve it in some way.

Highly appreciated!

Answer 1

After some careful analysis, I have found the answer to the problem. To be honest, as most things are, it was quite simple in the end. The lpsolve55.dll wasn't recognized because I didn't have my new bin-folder in the Path, which I did have with my old project. I simply forgot.

On a further note however, after the lpsolve55.dll directory was added to the path, I still got an error telling me there was no model to be found that could solve my directive. Since the error occured when I was calling the LPSolverDirective(), some research landed me on the following page:

http://lpsolve.sourceforge.net/5.5/MSF.htm

Above page gives a complete and stable way of how to acces lpsolve55.dll using the LPSolverPlugin straight out of Microsoft.Solver.Foundation.dll. After following the method in the link that involves editing my projects' bin/Debug and bin/Release folders, I got the LP model up and running within no-time.

Morale of the story - read the documentation. I am a bit of a beginner in programming entire multi-project solutions and using customly-added dlls, but hopefully this helps someone else experiencing the same. In the end, I learned a lot by simply trying different methods of getting it to work, so no time was wasted.