Neither DVD-R not DVD+R can be erased, you should use the RW (rewritable) version for this.
I always use DVD+R and it works flawlessly. There are some threads in these forums explaining the difference (one of the Read First threads in this forum contains a link to an article about the differences).
Posting your question more than once is not appreciated around here; deleted the other one. Finally, please use a more descriptive title next time, "Please help" does not really tell what your problem is about and people may, as a result, overlook it.