Product:
Cognos Controller 10
Excel Link
Windows 2003 Server
Citrix Server

Symptom:
When working in Excel with Cognos Controller link you get an error message.

Error message:
Standard Error
Number: 7
Source: mscorlib
Description: Execption of type ‘System.outOfMemoryException’ was thrown.
At System.IO.MemoryStream.set_Capacity(Int32 value)
At System.IO.MemoryStream.EnsureCapacity(Int32 value)
At System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count)
Xxx

Solution:
The Windows check if there is memory free that the application can use, and at this moment there is not enough memory free on client computer/terminal server, so this error is sent from the Windows Operation system, to not allow the program to access the memory.

In the case of Excel reports, consider to make them smaller with less amount of formulas.
Also ensure the client/citrix server have enough memory.
At least do you need 8 GB of ram on a citrix server, which should handle a few Cognos Controller users.

Run the same excel sheet on a computer/server with a lot of memory and see if the problem is gone.