Index was out of range

Hello, I am going through the developer tutorial. I have completed section 4 but “Checks” is showing an error. Failed to build project. Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: chunkLength From this I presume that an array in the underlying code has an out of range index. But whereas previous errors have shown up in Mendix Studio as red dots and so there is a clue as to where to look, here there is no clue where to look. So how do I fix this? Which leads to what is the approach for bug fixing in Mendix? I could delete the work done in that part of the tutorial until checks is green but that seems a bit clumsy. I have looked at the “What are checks” video but that is very high level. Also looked at the Checks → Consistency errors in the docs. Any ideas?  
3 answers

I have the same problem too. Because I am super frustrated at the moment, the tone I use here is not as kind. I am deciding if Mendix is a viable choice for me and my team at a large consultancy firm. We currently use and partner with OutSystems and Microsoft on the Power Platform. I feel as if I am wasting my time on these Mendix tutorials. I am sure the real world use case is a much better experience, but since I am the key person deciding on low-code platforms; I need to have a good experience here to build my confidence before making recommendations about the Mendix platform for my peers. 

For me, the problem started when the tutorials demanded version 9.5.0 and almost immediately when opening the project; it faced me with the attached error below. Then I upgraded to 9.15.0 and I suspect the UPGRADE to the project produced this error we’re discussing.

I then created a new application using the 9.15.0 template and life is good, with no checking errors. The issue here is once again BAD OLD 9.5.0 tutorials using an unsupported version. I sent in an earlier ticket 154069 and it seems this version issue about 9.5.0 continues to bite me in the rear end.

If Mendix does not want to invest the time to help folks learn thier platform, then I do not want to waste my time learning it, and being frustrated over what should only be problematic based on my inability to follow along.


I am blocked because I can only proceed using 9.15.0 and I do not want to invest more time only to have issues further down the road NOT using 9.5.0. I would expect to proceed without incident as 9.5 to 9.15 seems like only minor revisions and not 9.0 to 10.0 but again I am very selective with my time and until someone from Mendix can assure me that proceeding with 9.15 despite the requirement for 9.5, will be ok; I’m going to pause investing any more of my time.



Thanks Van!

I figured out the fix – STUDIO IMO is buggy as not only does this issues herein exist but the QR code is unreadable to 3of my android apps – the next issue past this one.


CORE issue is the tutorials and Mendix not monitoring the course to ensure its current with the software – PAINS of CI/CD…


This issue here in is definitely related to the 9.5.0 mandated tutorial version and some future decommissioning of the version being supported by STUDIO. When studio upgrades the app it is falling apart and does some bad steps. 

To fix open it in Studio pro. I saw two warnings about the nav menu and the home icon set to DO NOTHING so I told it to OPEN the page HOME as contextually it makes sense. Then publish and BAM the app magically works in the STUDIO web version IDE. 

Also the QR code generated in the desktop app Studio PRO works perfectly but the online WEB Studio does not – takeaway for me is AVOID the Online STUDIO IDE as its not worth the aggravation. Sadly the tutorial sends you there 1st.

So in the end I fixed the issue because I could, but I am a seasoned low code developer. I wanted to explicitly follow the same tutorials, so I subject myself to the same steps my staff would endure. They may not be so knowledgeable or adventurous to resolve the issue as I was. Mendix should address this serious issue. 

I very much appreciate this community and your offer. As with most platforms, the 800lb gorilla who owns the product rarely shares the same passion as its community of users. Problem is when you are charging customers top dollar, you need and expect answers to come from the software owner, not its community.

Aside note; the default 9.15.0 Mendix template with nothing done is remarkably similar to and at a fraction of the Mendix cost. My ignorance is high with Mendix, but this is in my mind strongly as I evaluate the value and responsiveness of Mendix wholly.

If I were using this for a personal project or me as a side hustle, then the community support would work, but again I am evaluating Mendix’s ability here and was hoping to see them chime in. and take action.


Unfortunately I don't have an answer for you as it seems like an error you might not be able to fix yourself. Someone else had the same error but no solution was found on that thread either.

Since this seems like a platform error, I'd recommend submitting a ticket to support. They should be able to help you!