We finally resolved our issue by upgrading to DNN 4.4.1 along with a then-beta copy of the module (beta version 3.1.11 graciously provided by Steve Fabian -- thanks again, Steve!). 

We are currently runnning DNN 4.4.1 with Repository 3.1.13 and have not had the "arithmetic overflow" issue since going to DNN 4.4.1 and the newer Repository versions.

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esmamlin atxgeek.me

The following as an FYI; DNN 4.8.2, using the App_Data provided db. The currently released version of the repository gives me errror 'Index was out of range.... blah blah blah'. Its disappointing to see this error persist. It could be the configuration that causes it but still, the whole point with these modules is to have their base behavior up and running with minimum effort...

I too also came accross this error:  "Index was out of range.  Must be non-negative and less than the size of the collection.  Parameter name: index."

I no longer get the error but here's some details below of how it happened:

DNN version: 04.05.05
Repository Version: 03.01.13

Occurred at least 3 times whilst uploading 2 different PDFs (uploading as an Admin user)

I changed 2 things - checked the ALL box for categories(when uploading), and checked the box for 'All Users' under Security Roles in Settings.

HOWEVER,  when I tried to induce this error again by undoing the above - I couldn't. I just can not replicate the error at all and havn't changed anything else. I even uploaded the exact same PDFs and now it is ok!

So not sure if this helps anyone solve this problem or just confuses the issue even more.
If anyone still gets this error, I would try creating another repository module, upgrading the repository or changing the settings somehow.

mark.