How to downgrade libc6 ?

[Markus.Grunwald@pruftechnik.com]

Hello,

today, I aptitude installed apache2, which took a new libc6 with it.
Now I can't link against one of my libs anymore:

/usr/local/lib/libcpdbg.a(cpdebug.o)(.text+0x374): In function 
`dbgSprintx':
: undefined reference to `__ctype_b'
./lib_x86/libtabe.a(tabe_zuyin.o)(.text+0x7c): In function 
`tabeZozyKeyToZuYinIndex':
: undefined reference to `__ctype_tolower'

I might be able to recompile it, but this could take a long time so I may 
be forced to go back to the elder libc6 - unfortunately, I don't know 
how...

Please help me, or I am in deep trouble...

TIA 
Markus Grunwald