Hello Ludek,
Thanks for your answer.
Actually the problem had happened before but rarely, and it has been happening with more frequency in the last few days. I suppose it is due to the fact that the number of users has increased.
I think I didn't find exactly the problem I have in the articles of the site, because in this case one report can work many times with similar parameters, and suddenly it can fail, working again with the same parameters after restarting the IIS.
Since CR XI is out of support (I had read your article but I had the doubt if CR XI R2A was still being supported or not) I suppose that I will have to modify the application to bypass this problem. I think it would be possible, because the data source of the report is a DataTable that is populated before the report is loaded. Some parameters are passed to the report itself, but this can be changed. The idea is to eliminate the parameters from the report. I suppose that should work.
Thanks
Geronimo