A contractual or non-contractual liability for damages on the part of protel, its employees and vicarious agents exists only if the damage is due to gross negligence or intent. Any mandatory liability under the aspect of the absence of a warranted characteristic, an at least slightly negligent breach of a material contractual obligation and for any defects of title remains unaffected. protel is liable for damages for which it is responsible up to the total amount of the system price to be paid in accordance with the order (protel licence fees plus protel service fees), whereby the liability is limited to the licence price if the liability results from this or to the service fees if the liability is related to this. The fees applicable at the time the claim arises, excluding VAT, are decisive. protel is not liable for lack of commercial success, indirect damage and consequential damage and for damage arising from third-party claims, with the exception of claims arising from infringement of third-party property rights. protel is only liable for the recovery of data if the customer has ensured that this data can be reproduced with reasonable effort in the sense of proper data processing from databases that are kept available in machine-readable form. An external backup of the database at the end of each working day is justifiable. protel is not liable for damage caused by contractual products if this could have been avoided by checking the work results of the contractual products at regular intervals. Furthermore, protel is not liable for damage caused by the use of other programmes that can change the data stored in the protel programmes. Any mandatory liability under the aspect of product liability remains unaffected. Claims for damages against protel, with the exception of claims for damages in tort, expire in accordance with the statutory provisions, but no later than two years after installation of the relevant protel programmes at the customer's premises.