Payment method error. Upgrade from 2.50 to 2.60

Hiya,

I've created a payment method for the dutch payment provider iDeal. It was working perfectly in 2.50 but when i updated my shop to 2.60 i keep getting the following error (it also occurs when saving the new user friendly name):

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We're sorry, an internal error occurred that prevents the request to complete.

Our supporting staff has been notified with this error and will address this issue shortly. We profusely apologize for the inconvenience and for any damage this may cause. You might want to try the same action at later time.
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The project builds just fine, i've used the Deploy.bat and Prepage.bat files, no warnings and no errors. I've updated the Description.txt as well to make sure it's listed properly. But, of course, it does, otherwise it wouldn't be in the plugin list ;-).

I couldn't find anything in the release notes which could reveal the problem, nor did i find anything in other payment methods which could explain this error.

Do any of you know what i'm missing?

Cheers.

qck wrote:

To find out what went wrong you need to turn off the custom errors mode.
1. Open web.config file
2. Find out the following line <customErrors defaultRedirect="errorpage.htm" mode="RemoteOnly">
3. Replace it with <customErrors defaultRedirect="errorpage.htm" mode="Off">

You can also try checking the logs area in Administration.