I am using Wikispaces and didn't run into any problems... You can upload a spreadsheet with all the data and then Wikispaces walks you through the rest of the process.
Your question may have already been answered, but I thought I would share with you what I did with my 150 students using my wiki. The day I introduced my classroom wiki, I had the students in each class period come to my desk and type in their e-mail address so they could receive the invitation. They then went back to their desks where we were using a class set of lap tops and opened their e-mail and accepted my invitation. I would also reccomend creating a "dummy e-mail" so that students with no e-mail or computer access can still use the wiki using the e-mail and password you created. I use wetpaint for my wiki and this method for inviting students worked well for me.
James from Wikispaces here. Sorry to hear you're having trouble. Two options:
1. Use our bulk user creation tool if your students don't yet have Wikispaces accounts. It's purpose-built for educators who want to add lots of students to their wikis, whether or not they have email addresses. More on this tool can be found at: http://blog.wikispaces.com/2008/12/create-accounts-for-your-student...
2. The invite page -- if your students already have Wikispaces accounts -- lets you invite up to 100 students at once. Just paste all the email addresses into that box.
If there's something else you're looking to do, we'd love to hear about it and try and find a solution for you (and others with the same problem). Drop us an email at help@wikispaces.com.
Think this is probably my second reply - can't find the first one to edit!
As I am a university teacher (in Spain) I don't think I would be eligible for the bulk user tool, it being only available to K12 teachers.