While upgrading a Visual Studio 2010 web application hosted under Server 2003/IIS 6.0 to a Visual Studio web application hosted under Server 2012/IIS 8 I ran into an interesting problem. After installing the latest crystal runtime files on the web server I was adding the crystal reports one at a time which included an .aspx page with a crystal viewer and the appropriate .rpt file and things were working fine until they stopped.
To make a long story short, in one folder there are about 20 crystal reports. I got a couple of them working by creating the .aspx pages and copying over the .rpt files. Thinking everything is looking good I then copied the other 18 or so .rpt files to get them in place and then the web server would hang forever when requesting any crystal report. I don't know what the number of .rpt files in the folder was to start this issue but what I did in the end is to create a sub folder for every single report.
Even in the old environment I noticed certain report that seem slow to load especially after site updates were deployed to the web server. Now that they are all in their own folder the come up super fast comparatively. I don't know what happens but it seems maybe IIS has an issue compiling something when there are so many .rpt files in one folder? Not sure, there were no entries in the event logs and no entries at all in the web log files even indicating I ever requested an .aspx page with a crystal report in it.
So just an FYI in case someone else ever runs into this issue. YMMV