Since I updated my own tekkit to the newest version my forestry didn't work anymore so you will need to install the good Forestry version so you will be able to join the Tekkit server.
1. Download the good Forestry client version here
2. Add a zzz_ to the name so it looks like zzz_forestry-22.214.171.124-mcpc1.2.5.zip
3. Then remove your old Forestry and place the one you just downloaded and renamed here:
4. Remove the Forestry stub files from Equivalent Exchange: Remove the EE2ClientV126.96.36.199.jar