Button to open a window in CRM2011: Could not load type

I've created a simple ribbon button which opens a new ASPX page and passes some parameters to it.

I've placed the page along with it's .DLL files in C:\Program Files\Microsoft Dynamics CRM\CRMWeb\ISV\<My Web Folder>.

The ribbon button links to /ISV/<My Web Folder>/<My page>.aspx

But all I'm getting is a CRM error. If I look in the event viewer, I can see this:

Event code: 3006 
 Event message: A parser error has occurred. 
 Event time: 2011-04-21 11:23:26 
 Event time (UTC): 2011-04-21 09:23:26 
 Event ID: a2f50bca417344949bd8d0acde5e1c61 
 Event sequence: 1591 
 Event occurrence: 9 
 Event detail code: 0 

Application information: 
 Application domain: /LM/W3SVC/1/ROOT-3-129477829326577670 
 Trust level: Full 
 Application Virtual Path: / 
 Application Path: C:\Program Files\Microsoft Dynamics CRM\CRMWeb\ 
 Machine name: SRV-CRM-D03 

Process information: 
 Process ID: 1772 
 Process name: w3wp.exe 
 Account name: DEV\CRM 

Exception information: 
 Exception type: HttpPars开发者_StackOverflow社区eException 
 Exception message: Could not load type <Type of my ASPX form>
 (...)

I'm guessing CRM isn't looking for the DLL where it should. What's the solution here?

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Where did you place the assembly for the page? It should be in the binfolder of Dynamics CRM.

Please keep in mind that the ISV-Directory is officially deprecated and should not be used for new development. It is only there for backward compatibility. See how to Upgrade Code in the ISV folder to Microsoft Dynamics CRM 2011

Another option is to use HTML pages and JavaScript which could be deployed with a solution and could use the new REST endpoints.