Well,I'm no usual guest in here,but I think this problem will let your heads smoke a bit:

After I've installed a terrain mesh for Germany (not fm_allemagne.zip ,but the one from the italian guy), landclass files for Germany, german rivers (allocated to three folders) and some VFR objects (for Germany),FS tries to load and shows me these error messages:

There are no further scenery add-ons installed.
My 768Mbytes Ram plus a swap file of 2300Mbytes should be more than enough to load all that stuff.
After that,I tried to install the add-ons step by step: first the mesh,then the landclass,then the rivers.
After having installed the second "rivers" folder, the above error occurs again.
All those four folders together (mesh,rivers 1+2,landclass) contain 3225 files and the "pure" size of all my Germany add-ons together is about 90Mbytes, which corresponds with the size of Holger Sandmann's British Columbia mesh (this one runs w/o problems).

So now I've got the following questions:
1) Is there an upper limit for the number of objects allowed for add-on sceneries?
2) Can my System (specs in my signature) be responsible for that,too?
3) What can I do in oder to lower the number of objects? (like bonding singe .bgl files to a larger one)

Greetings,
Exploder (who just wants to do some VFR in his homecountry )

Problem solved.
Too many files in one folder/mixup of different .bgls from different stuff.
I've installed everything how it should be installed (addon for addon) and it works.

Lesson learned,case closed. Good night.