I have never heard of such an error message, does it really com from Limesurvey? If you are hosting it yourself, you are responsible for these limits.
Afaik Limesurvey Community Edition has no limits beyond the limits of your hosting environment or the limits of the database engine that has been used.
There is no specific caching plugin for Limesurvey as far as I know. However, this usually isn't a big issue, as long if you don't use massive files like huge images, etc.
What is your hosting environment? Shared hosting, VPS, dedicated server?
What does "slightly bigger load" mean? How many questionnaires per minute, hour, day?
To me, my first impression is that the hosting environment isn't powerful enough, but without knowing what hosting is used, what the package involves, etc. it is difficult to help.
But the error message doesn't sound like something from Limesurvey, but rather something that comes from your hosting provider.
A general bottleneck of Limesurvey usually are the rather big session files, especially when the survey is a little bit bigger.
So how much RAM, how much bandwith, what processores, etc. can give a first idea what we are dealing with, together with some details about what "slightly bigger load" means, etc. And of course a screenshot of the error message.
I answer at the LimeSurvey forum in my spare time, I'm not a LimeSurvey GmbH employee.
No support via private message.
